yes, but with the little statistics they have on second-hand sales, game developers can judge whether or not interest in a sequel is enough to justify expenses.
Not really. Indie developers
maybe, but AAA publishers will look at EoFY reports and make assessments from that. Remember that when you buy a game from a store, that store itself bought a copy from the manufacturer in bulk, who then sell it on to you at a premium. Any data about second-hand sales is too unreliable.