Do you buy used carts/needles? Is it risky?

Any cartridge once played is "used". Each album played front to back is about a 1/3 mile of cartridge wear...after 2000+ hrs all cartridges likely need a rebuild or a new replacement. I just had my rebuild service done by Peter at Soundsmith. If you find one you like on the used market– a rebuild is a great option at a price-point about a 1/4 cost of new; and they also make great in-house cartridges too. 

https://sound-smith.com/services/phono-cartridge-repair-restoration-tip-repair

Yes but, only exclusively from Japan. All the sellers I deal with are extremely honest and helpful when asked for additional information when needed. They also fully clean and inspect each cartridge before they sell it. Some special or collectable cartridges in less than perfect condition can be purchased for a significant discount. I've purchased a couple in this condition  eg. two SPU's with bent cantilevers and had them restored for the same amount of the price savings. Moreover, there are a lot of used or vintage cartridges that were only ever available in Japan which from my perspective here in Canada, is value added.

Risky?

My grandfather advised my mother, who passed this on:

"Only lend money if you can afford to lose it"

also

"Avoid losing a friend over money"

IF you buy a used cartridge, be prepared to lose once in a while, so far I haven't, but the odds are .....

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. 

About used suspension material:

old, brittle, soft, pliable, it is something to think about.

Steve Leung at VAS looked at me and said "it’s amazing how these Audio Technica’s suspensions hold up" I agree.

My several old Shures, the one Sumico, the one JVC Victor all have held up. Being close to VAS, I took a small batch of mine, Ray inspected, and cleaned into the recesses of the suspension.

One of mine had miniscule metal particles down in there, and I realized: I had it in my shop, I have carpet tiles glued on the workbench, and even though I always brush it clean, tiny metal specks are down in the carpet, and it's ..... magnetic!