<PAGE>

                                                                         EX10.23

================================================================================
                                  CONTINENTAL
                                    CAPITAL
                                   & EQUITY
                                  CORPORATION
================================================================================


                            195 Wekiva Springs Road
                                   Suite 200
                            Longwood, Florida 32779
                                     PHONE
                                (407) 682-2001
                                      FAX
                                (407) 682-2544

August 13, 1998

Mr. Fredric Rittereiser
ASHTON TECHNOLOGY GROUP, INC.
1900 Market Street
Suite 701
Philadelphia, Pennsylvania

RE:  LETTER OF UNDERSTANDING-AMENDMENT OF CLIENT SERVICE AGREEMENT

Dear Fred:

This letter shall serve to amend the Client Service Agreement (CSA), dated
February 20, 1998, between Continental Capital & Equity Corporation (CCEC) and
Ashton Technology Group, Inc. (the "Company"). Specifically, CCEC agrees to
amend fees and expenses due CCEC from the Company, as originally defined in
Section 4 of the CSA, as follows:

In consideration of services performed under the CSA and new consideration
provided to CCE  by the Company in accordance with the Letter Agreement between
CCEC and the Company, dated August 13, 1998, CCEC agrees to waive payment of the
monthly retainer fee of $15,000 for the months of September, 1998; October,
1998; November, 1998 and December 1998. Further, the monthly retainer fee due
under the CSA for the months of January, 1999; February 1999 and March 1999
shall be reduced from $15,000 to $5,000.

In addition, CCEC agrees to waive the payment of $100,00 cash bonus due CCEC by
the Company upon the Company achieving a listing of the AMEX.

All other compensation considerations due CCEC by the Company as defined in the
CSA remain unchanged.

If this is also your understanding, please so indicate by signing the space
provided below.

Best Regards,
CONTINENTAL CAPITAL & EQUITY CORPORATION

/s/ Dodi B. Zirkle

Dodi B. Zirkle
Vice President

Agreed and accepted on this 13th day of August, 1998.


/s/ Fredric Rittereiser
------------------------
Fredric Rittereiser, Chairman and CEO
Ashton Technology Group, Inc.

<PAGE>


                            ======================
                                  CONTINENTAL
                                   CAPITAL
                                   & EQUITY
                                  CORPORATION
                            ======================




                           195 Wekiva Springs Road
                                   Suite 200
                            Longwood, Florida 32779
                                    PHONE
                                (407) 682-2001
                                      FAX
                                (407) 682-2544

13 August 1998

Mr. Fredric W. Rittereiser
President & Chief Executive Officer
The Ashton Technology Group, Inc.
1700 Market Street, Suite 701
Philadelphia PA 19103

Dear Fred:

This will confirm the understanding and agreement (the "Agreement") between
Continental Capital & Equity Corporation and its affiliates ("CCEC") and the
Ashton Technology Group, Inc. and its affiliates (the "Company") as follows:

1.   The Company hereby engages CCEC as an advisor in connection with the
exploration of certain strategic and financial alternatives available to the
Company's subsidiary, the Electronic Market Center, Inc. ("eMC").

2.   CCEC hereby accepts the engagement and in that connection agrees to:

     (a)  become fully familiar with the business, operations, properties,
financial condition, prospects and management philosophy of the eMC;

     (b)  advise and assist the management of the Company and eMC in evaluating
certain strategic and financial alternatives available to eMC; and

     (c)  assist the Company and eMC in establishing the market acceptance of
     eMC through identifying and assisting in entering into agreements with
     users of eMC.

3.   The Company shall furnish, or cause to be furnished, to CCEC all
information requested by CCEC for the purpose of rendering services hereunder
(all such information being "Information"). All Information provided to CCEC
hereunder, to the extent of such information is not available, will be kept
confidential and be subject to a separate Confidentiality Agreement. In
addition, the Company agrees to make available to CCEC upon request from time to
time the Company's officers, directors, accountants counsel and other advisors.
The Company recognizes and confirms that CCEC: (a) will use and rely on the
Information and on information available from generally recognized public
sources in performing the services contemplated by this Letter Agreement without
having independently verified the same; (b) does not assume responsibility for
the accuracy or completeness of the Information and such other information; and
(c) will not make an appraisal of any of the assets or liabilities (contingent
or otherwise) of the Company.

4.   The term of CCEC's engagement hereunder as an advisor to the Company shall
extend from the date hereof through August 31, 1999. It is understood that this
engagement is an initial engagement and is renewable with the consent of both
the Company and CCEC. Subject to the provisions of paragraphs 4 and 5 through
11, which shall survive any termination of this Agreement, either party may
terminate CCEC's engagement hereunder at any time, with or without cause, by
giving the other party at least ten (10) days' prior written notice.

5.   As compensation for the services to be rendered by CCEC hereunder, the
Company agrees to pay CCEC a retainer of one hundred seventy five thousand
(175,000) shares of its common stock on the date hereof. In addition to this
retainer, the Company will pay CCEC an additional retainer fee of seventy five
thousand (75,000) shares of its common stock at such time that the Company
delivers eMC's business plan to CCEC. This retainer will be CCEC's full and
complete compensation for the services to be rendered hereunder. It is
understood that these shares will not be registered, however, the Company will
endeavor to register these shares at such other time as it may deem appropriate,
or at such time as other shares are registered on any appropriate Registration
Statement. It is further understood and agreed that these shares will be subject
to a "lock up" agreement and will be released from this "lock up" agreement
ratably; 6,9 and 12 months following the completion of a strategic financing of
a minimum of $15 million for eMC. In the
<PAGE>

event the strategic financing does not occur by August 31, 2001, all stock shall
be fully released to CCEC from the lock up agreement.

6.   In addition to any fees payable hereunder, the Company shall reimburse CCEC
and its affiliates promptly upon request for their respective out-of-pocket and
incidental expenses, incurred during the term and as a direct result of its
engagement hereunder, including the fees and expenses of legal counsel and those
of any advisor retained by CCEC. CCEC will bill the Company monthly for such
expenses. The Company shall not be obligated to reimburse CCEC for its
out-of-pocket and incidental expenses unless CCEC obtains written approval from
the Company prior to incurring any such expenses hereunder.

7.   The Company and CCEC agree to enter into a mutual indemnification agreement
as set forth in the separate letter agreement, dated the date hereof, between
CCEC and the Company.

8.   Any advice provided by CCEC under this Agreement shall be treated as
confidential by the Company and shall not be disclosed or made available to
third parties without CCEC's prior written consent.

9.   The Company represents and warrants to CCEC that there are no brokers,
agents, representatives or other persons which have an interest in compensation
paid or payable to CCEC hereunder.

10.  The benefits of this Agreement shall, together with the separate indemnity
letter, inure to the benefit of respective successors and assigns of the parties
hereto and of the indemnified parties hereunder and their successors and assigns
and representatives, and the obligations and liabilities assumed in this
Agreement by the parties hereto shall be binding upon their respective
successors and assigns.

11.  This Agreement may not be amended or modified except in writing executed by
the Company and CCEC and shall be governed by and construed in accordance with
the laws of the State of New York, without regard to principles of conflicts of
laws.

CCEC is delighted to accept this engagement and looks forward to working with
you on this assignment. Please confirm that the foregoing correctly sets forth
our agreement by signing the enclosed duplicate of this letter in the space
provided and returning it, whereupon this letter shall constitute a binding
agreement as of the date first above written.

CONTINENTAL CAPITAL & EQUITY CORPORATION



By: /s/ Dodi B. Zirkle
   --------------------------------------
Title: Vice President
      -----------------------------------


Agreed & Accepted:

THE ASHTON TECHNOLOGY GROUP, INC.


By: /s/ Fredric W. Rittereiser
   --------------------------------------
Title: President/CEO
      -----------------------------------