Here's whree to start
http://dev.mysql.com/doc/mysql/en/Binary_log.html It logs all updates to your databases. You can then build an app that validates the databases, for example does the payout match the total signups and were there any changes at the last minute.
Also if you're worried about your programmer, have another independent programmer audit the production code. Programmers can put some crazy stuff in their code if they think no one is looking