By mid-game, one of my characters always has Master Merchant skill with 15 points. This allow him/her to sell items in Suttersville at actual stated value and none of the Merchant there will buy it.I don't run around to other merchants because of this so was not aware that others might buy it.
Did you try to sell BG's Shield (BG's Shield has a nice AC, but there are far better shields available for my Priest) or any of the Ice Weapons. I never use the dagger or staff skill so the Ice Dagger and Staff are useless to me (I have never played MM6 or TCC with a Sorcerer). None of the merchants in Suttersville will buy them so I just stash any unused stuff in chests there in Sutter's Bay.