lol@you saying not to spam in a tec thread
there isnt a fullproof way that i know of but a compression test and cylinder leakage test would be a good place to start, also check the hoses and overflow bottle. if they look like they have been replaced reciently then ask why? maybe it had a cracked overflow bottle or burst hose at some time which my have cause it to overheat.
check that there isnt any signs of leaking coolant from the radiator, thermostat housing, overflow bottle or radiator and check the coolant condition.
and if it is a later model car with obd2 then check for old fault codes that could have been logged if it had overheated.
also do some research into common faults wiith the vehicle, overheater might be one of them, like 1mz powered camrys that overheat at the first sign of trouble.