<Page>

                                                                    EXHIBIT 31.2

CERTIFICATIONS

I, Francis S. Mascianica, Jr., certify that:

1.   I have reviewed this annual report on Form 10-K for the fiscal year ended
December 31, 2003 of Seacoast Financial Services Corporation;

2.   Based on my knowledge, this annual report does not contain any untrue
statement of a material fact or omit to state a material fact necessary to make
the statements made, in light of the circumstances under which such statements
were made, not misleading with respect to the period covered by this annual
report;

3.   Based on my knowledge, the financial statements, and other financial
information included in this annual report, fairly present in all material
respects the financial condition, results of operations and cash flows of the
registrant as of, and for, the periods presented in this report;

4.   The registrant's other certifying officers and I are responsible for
establishing and maintaining disclosure controls and procedures (as defined in
Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and we have:

     a)   designed such disclosure controls and procedures, or caused such
          disclosure controls and procedures to be designed under our
          supervision, to ensure that material information relating to the
          registrant, including its consolidated subsidiaries, is made known to
          us by others within those entities, particularly during the period in
          which this annual report is being prepared;

     b)   evaluated the effectiveness of the registrant's disclosure controls
          and procedures and presented in this report our conclusions about the
          effectiveness of the disclosure controls and procedures as of the end
          of the period covered by this report based on such evaluation; and

     c)  disclosed in this report any change in the registrant's internal
         control over financial reporting that occurred during the registrant's
         fourth quarter of 2003 that has materially affected, or is reasonably
         likely to materially affect, the registrant's internal control over
         financial reporting; and

5.   The registrant's other certifying officers and I have disclosed, based on
our most recent evaluation of internal control over financial reporting, to the
registrant's auditors and the audit committee of the registrant's board of
directors (or persons performing the equivalent function):

     a)   all significant deficiencies and material weaknesses in the design or
          operation of internal control over financial reporting which are
          reasonably likely to adversely affect the registrant's ability to
          record, process, summarize and report financial information; and

     b)   any fraud, whether or not material, that involves management or other
          employees who have a significant role in the registrant's internal
          control over financial reporting.

Date:  MARCH 11, 2004


/s/ Francis S. Mascianica, Jr.
--------------------------------------------
Francis S. Mascianica, Jr.
Treasurer and Chief Financial Officer
(Principal Financial Officer)

                                       107