A few years ago, I sent a worn MMC5 I'd gotten off ebay to FJS @ tonabnehmer/schallplattennadeln. He gave me instructions on sending the cartridge to him and various options - I sent it tracked and it showed as delivered but then I was ghosted and never heard anything else back via email. I only lost 35 bucks or so, plus the shipping, but I'm still pissed about it. I only wish I had gone through ebay and not via direct correspondence, maybe I would have had recourse through ebay at least.
I ended up getting an SMMC4 about 6 months ago after the price seemed to drop down to 200, and i'm pretty happy. it doesn't sound the best on inner grooves on my RX2, but i otherwise like the sound signature (it's definitely brighter than my still-good MMC2 on my TX2)