The only used tub worth the money to move is if you can see it filled, working, and heated up before you arrive to inspect it. A drained tub might not only have been improperly winterized causing freeze damage, it also possibly has a few dried out seals which will need to be replaced at the least.
I watch the used market weekly. 95% of the tubs out there I see are junk not worth $100 with the repairs needed. Very few (about a handful a month in my region) pop up in fully working condition, and of those, only about half are a decent name brand tub worth the price they're asking. But that's just my $0.02 as a spa enthusiast, I am by no means a professional.
