Yes, follow the good advice given, and, above all, don't overpay.
Second-hand photogear and materials usually has very little value, simply because of lack of demand. The original cost has no real bearing on the current value, neither has the asking price of similar gear at a dealer...he has all the expenses and overheads to cover, as well as the risk of not selling for what he hopes, and the liabilities of offering a warrenty.
It sounds as though you might be taking a lot of stuff which you don't really need, just to get the few items of use. Fair enough if you're happy to do that as part of the deal, but you're probably doing the seller a favour and giving yourself the hassle of disposal.
I recently bought a couple of s/h furniture items on E-Bay, in as new condition, from the same range and matching perfectly with my existing furniture. The price was small change, less than the cost of petrol to fetch them...the sellers just wanted them "out-of-the-way", yet they were quality items which would have been very expensive new. Things are only worth what someone is willing to spend at that point in time.