Here's something I can offer....

When it comes to used equipment, expect nothing. I always buy with return guarantee of some kind and check everything before it expires. You can try to profile the seller but it IS a used equipment you are buying. Despite the best intent, things can go wrong. (and does sometimes) This is awfully important when you are tight on budget. If something IS wrong and you are stuck with the gear, your options are extremely limited.

I always wonder why, when seller says he/she checked the gear but still offer no guarantees.