I would definitely try to politely inform them of their mistake. It would really be a shame if someone spent that much money, but then again, anyone serious about a pastel ball python would know that they were mislabeled. Definitely bring in some pictures and find sources listing the green eyes, etc., as pastel traits.

If the snakes look skinny... as about their feeding schedule, what size feeders they are fed... any respectable pet store should be willing to tell you. I tell all the customers that come in where I work exactly what the snakes are eating, and when, I'll even take out the schedule I keep hanging on the wall where I write down all the info for each feeding. But I'm just OCD like that I want people to know that the animals are eating well, it helps a sale. I don't see how some pet stores think that by skimping on care, they will make money. The best way to get and keep customers is to keep the animals in the best care and health possible, so you can insure happy, repeat customers. I would feel way too guilty to sell someone a sickly looking animal.

And as long as you keep your cool, theres no reason why you should be prevented from frequenting that store, unless by your own conscience.

I wouldn't give up... think about those poor snakes.