Oltronix B32-10 Laboratory Power Supply. Sold on Ebay as 'defective'. further stating, that 'voltage breaks down about mid-range'. There were even photographs with real good resolution. Looked at them, determined that the recessed front panel pot for the overvoltage protection (crowbar) is set about mid of it's adjusmend range.
Bought the unit, set crowbar to full CW, tested: GO.
Rohde&Schwarz Power Supply NGR20 on a Ham fleamarket, the seller started fo fidget when asked if it works by someone he obviously knew. Originally, he wanted 100€ for it. I jumped in, paid 40, came home, looked at the unit, moved the slide switch, which selects Sense int/ext two or three times to and fro: working flawlessly since then.
Siemens Multizet A1001 DC electronic multimeter, advertised as defective 'doesn't measure'. Was shown to switch on and give range indication on the secondary LCD. This LCD has a fuse symbol, which is shown when fuse is blown (or missing). This was clearly lit. Got the instrument, checked fuse (missing), replaced with the untouched, original spare fuse from the spare fuse holder: working, all nominal and within spec.