Generally speaking, I will never go in a mega-stop, for the very reason the OP states. But if you have too, look at the fuel island on the way in and if you can, get behind a local driver. In almost all instances, he wants to get his fuel, DEF and receipt and get out. He/she is not going to dawdle around.
If you scan the area, you will almost always find a mom-N-pop fuel stop near the megas and the price will usually be 20-30 cents lower per gallon. The locals know them and the stops are usually clean.
You drive through a Love's, Crooked Hook, T/A and the parking lot is full of trash with trash barrels sitting right there next to the trash. Looking at the grossly fat slobs that roll out of these trucks will tell you that they are too lazy to get out and put their trash in the receptacle. It's easier and requires no energy to simply drop it out the window for some other person to pick up.
Gone are the days of the Professional Driver. This new breed out here are a scary lot.