how much do spears experience wear and tear with typical private use over a period of a couple of years?
Not that much if the owner is responsible. You can usually tell by looking and a quick demo if something is wrong. (scuffs? Looks like it's been dropped? dustcap or tweeter dented?)
Dealing locally is better because you can usually demo them before forking over the cash. If the seller won't let you power on and listen for a bit before buying... well, stay away. But if you ask for a demo and they say OK, it's usually almost moot because they know it will be fine.
I have never had a real problem buying secondhand, and have done so quite often. I actually try to avoid buying new whenever possible.
The moving parts of a speaker typically last a long time, 20 years or so. The surround and spider may dry out and lose flexibility after a while. The surround can usually be replaced for not too much $$. Capacitors sometimes go bad in crossovers, which can also be fixed, but maybe not as cheaply. Those also tend to last >20 years, but can start going bad around then.
2 years is really nothing in terms of speaker wear/tear unless they really abused it somehow.
