Context is definitely important, yeah. It's normal to see an artist draw over the same lines and use the body as a template, but usually something changes (such as hair/ears/tails). I don't know how often they'll sell a straight up recolor though, I believe it's considered less acceptable unless it's being done for super cheap adoptables.

That is a downside of the adoptable market is that entirely enforced through social capital and good faith. You can't always have a set of clear expectations and rules.