I live in Texas. I'm disabled. I usually pump my own fuel anyway. There are all of 4 (I think) full-service stations in town, and two of them have ripped me off when I asked them to give me the handicapped discount. I decided it was easier to do it myself than go through that again.
There is no such thing as a "handicapped discount" at a full-service pump. Either you are at a full-service pump at a higher price or you are at a self-service pump at a lower price. If you are handicapped and want to pay the self-service price, pull up to the self-service pumps and ask for assistance. The ADA mandates that they help you.