I actually have to say I agree. It sounds like they are trying to hide something. And, I too bought a snake with an RI, and she ate through the whole course of it, so not eating isn't a very good indication. I probably wouldn't have known my ball python had an RI if I didn't hear the popping and see the mucus all over her hide three days into owning her.

Although, if the employee or owner is okay to hold the animal while you examine it, there shouldn't be an issue. If the snake was being starved you would know just by looking at it. If they can't offer to take it out for you, then that would indicate a big fat no.