It may make sense to hit the used market for the following categories:
a)
"High End": Typically, a 60k speaker can be bought for 30k and so on...guys who buy such speakers tend to take care of them. When your done with it, you can sell it for about the same price and cut even. If you bought speakers "new" in this category, you are never cutting even when you sell it (that’s a big L each time and doesn’t make much monetary sense).
b)
Rare: There are speakers that are quite rare and coveted (could be high end or affordable). A few units of a model were made, got discontinued in a short period, etc. It may make sense to look for those in the used market.
For either a) or b), go with an established manufacturer... If something goes wrong, you can get replacement drivers, parts, etc from a manufacturer who’s been around. If you bought something from a self proclaimed "exotic manufacturer" dude working out of his garage, you may be out of luck.
Otherwise, what’s your budget? At any normal/affordable budgets for speakers that aren’t rare, you can find something ’new’ that will beat the daylights out of some guy’s used crap (as speaker tech and designs improve every few years).