Since sure clients probably do not have FileMaker installed on their systems, you'll need to work out a way to provide an electronic copy of the data that they can review and comment on the information.
You could save a PDF and it is possible to "mark up" the PDF with comments so you can send out the PDF and get it back from the client with their comments and approval.
You could publish your database to the web. Clients would log in to the database via their web browsers to review the data and you can provide fields in a related table for logging their comments and approval. You's use accounts/passwords to limit which records a client can see and review.
If you do a lot of repeat business with the same customers, you might use FileMaker Advanced to set up a small runtime solution that you distribute to your clients. YOu then email them a small database file of their information to drop into this folder, replacing the previous copy of the file that is bound to that runtime application. They then can open the file, make comments, log their approval and can then email the file back to you where you import the data from that file into your main database to log their comments and approval.
Thanks very much! The runtime solution is definitely a possibility.