I picked up 2 females at the same show, and I fed mine the same day. Some snakes will not eat right for a while after they get moved around, and some that will not eat, will eat great after they get moved around. I never once waited to feed an animal after I bought it, and I never once had a problem with an animal that ate the same day I recieved it.
If it's a small Ball try live hopper mice (dark & light colored ones). If it acts shy towards the mice then try a smaller meal yet, some babies are too timid at first to take a larger sized meal. Just keep trying, I'm sure it will start eating fine for you.
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Chad Bachman