I have a customer who has thanked me for doing a great job on her home purchase with a gift certificate for $50.

I would like to do the same for her (JC Penney gift certificate), because she was a very nice person and felt it would be appropriate to thank her as well.

Can this be construed as a RESPA violation of any sort? Years ago I routinely would do this sort of "thank you" to clients after purchasing homes.

Any gift to the borrower would not present a RESPA issue. If you rewarded one of the other service providers in the transacton, i.e., real estate agent, that is when you start having problems. Check your bank's code of conduct before accepting the $50 gift certificate from the customer. It could run afoul of your bank's policies enforcing the bank bribery act.