Used amps, how to tell if,,,,,,,,,,,,,,,,,,,

I'm interested in buying a used amp and I an only afford  $2,000.00

I'm looking for an amp with at least 100 watts and decent or good or high current. Magnapans 7.1

I've seen some interesting amps circa 1980's 1990's but,

I was wondering how to tell if it's not sounding "right" to me  due to old caps.

1) what would be my recourse?

2) How would or could I tell?

ie if the caps are old how would it affect the sound?

thnax.