It may be more cost-effective and convenient to have both with one company. You and your office staff will be required to demonstrate equal measures of tact and firmness, understanding and confidence, in order to deal with clients who will range from confused to irate. The importance of advance preparation and skilled diplomacy should not be underestimated. When the Call Comes . . . Sooner or later, you will receive a call from a client who complains that you overlooked or didn't clearly explain something.
People can be understandably upset.
Express your concern and understanding. Offer to explain your report or your findings in better terms. Revisit the site if necessary. Often a new explanation on site demonstrates why you wrote your findings the way you did. Ask what the client would like to happen.