No...you should not have paid. Your deal with the dealer was done when you removed your firearm from his store. While it was in poor taste to do the FTF sale in front of his store, it was still you that made the sale, not him. Sounds like he may have been just trying to pressure you into giving him a cut. Also sounds like he's been taking advantage of you all along. More than one good reason to find another place to do business.