I got him Saturday and he is refusing any food. I tried flakes, 3 different types of pellets, and FBW. He is flaring up a storm in his 2.5 gallon, he sees me, he loses his coloring, gets stress stripes, and hides until I go away
Saturday wasn't that long ago, he might just be a slow settler. Try live or frozen. Most bettas will find it very difficult to refuse them.
I think sometimes bettas get treated roughly at the wholesalers and then roughly at the store and so they don't really have much experience with people beyond that.
However, I too have regretted purchasing certain bettas almost as soon as I walked out the door with them. I don't like having tanks filled with fish I don't particularly have an affinity to. In the past I usually just sold those fish on.
I've had this happen. Sometimes they get so stressed out from being moved and being in a new place that they don't even want to interact with you. It's like they get depressed for a few days or something. I'm sure he'll warm up to you. Some of mine don't like the camera either.