I personally would spend the 85 bucks on a new '57.

SM57's are work horses, it's true, but they CAN be beaten to death. You won't know what you're getting until it arrives and you test it. Just to save the hassle of re-packing, sending it back, fighting with PayPal for the refund and repeating the process until a decent mic comes along is worth the extra few dollars.

For that kind of cost difference, I'd buy new.
The only used mics I've bought so far was a pair of AKG C391Bs - from eBAY. They sounded quite different from each other and I intended to use them as a stereo pair, so I sent them to AKG to have them checked out.

They ended up exchanging both capsules (which wasn't free) - but I still saved a couple hundred from buying new. Unless there's enough of a savings to cover some rework on a "well used" item, I buy new.

I've purchased a lot of used Mike's. I've purchased a lot of new Mike's. I've never purchased any used microphones from eBay. Cheap microphones are best purchased new. Expensive studio microphones are worth a look at when purchased used. It's a crapshoot.

Snake eyes
Ms. Remy Ann David

I've bought a few used mics on ebay:

AKG D12
Beyer M201 x2
Beyer M101
Shure Unidyne

No dud ones yet, but I'm always careful to avoid sellers with less than pristine feedback, and all but the D12 were cheap enough to be well worth the gamble. ;)