Hmmmm.
High-Pressure Negotiator doesn't actually say "swap," and the word "swap" never appears on the Merchant card. So, if you're sure about that wording, maybe you mean another card.
Anyway, that Merchant ability lets you change which Items you are using (i.e., if you were using one Armor Item, and were carrying other Armor Items, and you decide you want to use a different Item, so you switch which one you are using), and it allows you to trade with other players, both during combat, which is normally illegal. A trade between two players can involve one player giving another player an Item or Items and receiving nothing in return.
What
High-Pressure Negotiator does
not let you do, is take an Item back to your hand, which is what I'm inferring you were trying to do. That's is the Explorer's (from
Jump The Shark)
Resourcefulness ability, which doesn't talk about swapping cards, either.
As for the
Cheat! question, it's easier for me to just point here, at this point, rather than try to explain (or remember) it all:
http://forums.sjgames.com/showpost.p...22&postcount=4