Not to try and be unpopular, but myself running an independent secondhand shop (video games and the like) I've banned customers before for doing exactly this kind of thing. This kind of vulture behavior literally steals business away from independents, whose overheads can be rather shockingly high. In my view, only if the selling customer categorically rejects the offer made by the shop and the shop won't go any higher is it ok to approach the person and make an offer on their gear, out of the store premises. Otherwise you are going into another mans shop and setting up camp trying to buy and sell where he is paying rent.
*And with that rant over...*
These are some bloody gorgeous 35mm bodies on here!
The Konica Eyeborg does have a look of the Cylons about it though...