Traders trading ability Q's - Star Munchkin

[Diseptikon]

So is it correct in assuming that a trader can repeatedly use their trading ability to take the top card immediately after use thus keeping powerful cards in their hand? If a player were so inclined, could they discard an item to bury said powerful card so that it effectively blocks the trader? If yes, can this only be during their turn?

If there are two traders during a game who gets priority in trying to utilized their trading ability? Would this simply be done by a roll-off?