Over the last 4 or 5 years I've bought a number of welders and a couple of plasma cutters at auctions. Some I resold in order to pay for the ones I decided to keep along with a few other tools and such. Here's a list as well as I can remember it:
Lincoln AC 225 Lincoln AC/DC 225/125 Lincoln SP-170T Lincoln Idealarc 250/250 TIG
Millermatic 185 Miller Econotig (Actually rebadged as a Mac Tools TIG welder)
Thermal Dynamics Pak 5XR plasma cutter Hypertherm Max42 plasma cutter
Of those I only had trouble with 2...
The Lincoln Idealarc had a big glob of metal melted across the contacts of the polarity switch where someone had apparently switched it while welding. A file cleaned it up easily and it worked great after that. (Technically I never actually owned this one. A friend loaned it to us so my son could learn to TIG and then I sold it for the friend)
The Miller Econotig looked like new and supposedly had only about 50 hours on it but the arc start didn't work. Turned out the output cap on the arc start circuit had apparently shorted out, putting welding current through the HV transformer and melting it. I fixed it myself but the parts cost me about $200.
All of the others worked perfectly and I still have the Lincoln AC/DC
225/125, the Lincoln SP-170T and the Hypertherm Max42.
I've passed over a few at auctions that I didn't think were worth the risk. There was a Millermatic 185 I probably could have gotten for about $250 but someone had removed the cover and never put the screws back in which is a BAD sign. I also won't buy anything if the plug has been cut off the cord unless it's REALLY cheap. That's often done on bad equipment so that no one will plug it in and make smoke or hurt themselves.
I'm usually pretty handy at fixing things and for the most part the units I've bought have been older technology transformer machines and there isn't much to go bad in them. Newer, fancier units have more components that can fail and are probably more expensive and difficult to fix so I've stayed away from them so far.
Best Regards, Keith Marshall email@example.com
"Even if you are on the right track, you'll get run over if you just sit there." - Will Rogers (1879-1935).