I was sure I was on track to buy a used AG pool but I've heard (well my wife has) stories about that not being a good idea and the pool falling apart prematurely.
I'm very handy and very capable (with online help and tips) of installing an AG pool. So I don't expect it to be my poor installation that would be the problem.

ADVISE please, I plan on buying a used (7yrs old or newer) 21ft Aluminum and resin pool. Is this a good idea?

Also...
Do the uprights (once the ground is fully level) need patio stones underneath them for extra support?