I always assumed "backdoor" sales meant closing a sales thread by stating "gonna keep this one for now" Only to find out later on that it was sold to another member. This happened to me on a gen forum when I tried going for a gen Tag Aquaracer and the douchebag stated "sold" then I see it up for sale by another member 2 months later.

I've never encountered this type of backdoor dealings. I'll be sure to keep an eye out for it but who in their right mind would buy into it anyway? After-all we're geeks not gullible. =D