Several thoughts come to mind. Where did you learn about the equipment? Is there a known dealer with a good track record selling the same equipment? Have you seen photographs and serial numbers? The only used equipment I have purchased (years ago) was from established dealers with published return policies so I was able to test the equipment (lenses). Fortunately they were as represented and still function perfectly. This was before EBay etc.and what seems to go on these days. ASs the saying goes "buyer beware".
http://www.jeffreyglasser.com/
http://www.sculptureandphotography.com/
http://www.jeffreyglasser.com/
http://www.sculptureandphotography.com/