Need advice on buying used system

the main thing that kills motherboard / cpu is heat (and sometimes bad luck) ive got a 15yr (maybe older) old 233 i keep running if its built well and has good ventilation a pc "can" last until the metal starts to corrode and or capacitors blow,

on the same note a brand new pc i was working with after the owner decided to clean it was fried due to a small amount of liquid propellant that came out of one of those compressed air canisters right into one of the processor terminals.