We always try to price off either GPA or eBay, or some combination thereof. Those tend to help dial in market pricing at that time, at least the eBay prices tend to estimate what people would pay if we put the book on the site (adjusting for fees of course).
There are always different motivations for pricing a book a certain way. Acquisition cost, geography, expenses, and personal biases towards what we think are cool all come into it. As for us, we like to move product while insuring we can afford to stay in business.
I’m still not convinced that a lot of these prices are sustainable long-term (especially in the variant market) but for now this is the sandbox we all get to play in.