Your right, with any of them, you have to find the buyer that wants what you have. Depending on how you sell, you may have an easier time here than someone else. I usually sell on consignment at a couple of local shops, and have had good results doing so. If you dont have the coverage/exposure you get selling through a dealer, or GB etc, then it will probably be a lot tougher. But with someone who has a lot of people moving through, I doubt it would be a problem.
Ive seen, and sold myself, guns that were "different" than factory, and they always seemed to go pretty quick, and not at a loss any worse than a factory gun Ive sold. In some cases the "different" guns made more because of the modifications. What does amaze me is, that guns with some of the aftermarket "junk" people put on them, sell like they do. These days, looks seem to be more important to some than function and quality.
Other than a few specific "factory" guns (HK's and Colts mostly), rarely have I ever made back close to what I paid for them when I did sell them. Its just the nature of the beast.