The timer thing is real, peeking kills the rise.

Bring a set of gauges and a multimeter, that is really the only way to know before you pay. Hook the gauges up right there in his driveway and watch how fast it pulls down, a good one will hit vacuum in a minute or two. Put the meter on the windings too, check for ohms and make sure nothing is grounded out to the shell. If the guy won't let you test it, that is your answer right there, just walk. Learned that the hard way myself after getting burned on a used one that "worked great".

Did the 12 euro one from the hardware store have a brand name on it, or was it just some no name thing? I ask because the cheap ones I keep finding all look the same but some clearly hold up way better than others. Was it a plain plug shape or one of those universal ones with the sliding parts? Those slider ones always seem to be the ones that crap out on me.