A few months ago I started providing escrow services, and did so free of charge. Of course many clients sent me tips but I want to be clear; I wasn't doing it for the money. My original motivation was to prevent naive newbies from getting scammed.
My suggestion would be to donate these tips to a good cause. You realized you were doing something in the grey area and have stopped.. but any money received as tips from these people remain tainted and a burden on your name.