I have bought both used and NIB, and each situation dictates the way to go assuming the pin is a current production model in distribution. My AFMr LE with pre-owned (single owner), because I was late to the game and I could not find a NIB option. Great seller, perfect machine, and would not have changed a thing. With my latest JP Prem, I was first looking and pre-owned thinking I could save a little, but after calling several distributors it was actually about the same price (even less than many of the JP's within driving distance) to get NIB.
Benefits of NIB to me:
1) Warranty
2) Backed by distributor if any issues occur (I had a few small issues with my JP that my distributor addressed for me immediately)
3) You're guaranteed to get everything that should come with the pin
3) Delivered to your front door
4) Don't have to deal with travel, cash transaction, truck, load/unload, security concerns, etc.
5) Call (don't email or look at website) for a quote. Most distributors are not permitted to advertise their actual prices so you may save a little, maybe get free shipping, and possibly no sales tax if distributor is out of state.
Benefits of Pre-owned to me:
1) Get the pin now instead of having to wait for availability and/or shipping times
2) You control the freight process, so you can be careful as possible during transport
3) Pin is most likely in full working order as the original owner would have taken care of any issues
4) Pin might have accessories/mods installed that would normally cost extra if purchased NIB
5) Might get a slightly better price, but often on new releases this is a wash or used may even cost more
6) Pay cash and might be able to negotiate on price a little