IF you buy a used cartridge, be prepared to lose once in a while, so far I haven’t, but the odds are .....
@elliottbnewcombjr Yep, that’s my philosophy too! I’ve also had many transactions and no mishaps so far. The savings over buying new from dealers has been huge. It's the only way to experiment and truly find your cartridge spirit animals. In fact, buying MC cartridges has been more reliable and fruitful for me than ANY other component! Shipping is cheap and reliable. @neonknight had some great pointers of what to look for when buying. I use many of the same rules. Also make sure you can distinguish between detritus that cleans up easily versus corrosion - all the iron bits corrode very easily, especially in humid environments (bad climate control, beach homes, etc) or with sloppy users.
There are some "dealers" who move a lot of used carts that are fine to buy from (TMR, Wayne’s Audio), and others that have a less than sterling reputation (buyer beware; check feedback). But the best exchanges I’ve had have been directly from fellow hobbyists.



