It sounds like false inflation to me also. People have been doing this with various things lately, and it's a very very dirty way of making np. Protect yourself by always checking *both* the TP and shop wiz on trade offers, checking the rarity of the item, and if something still feels fishy insist on pure.
Often these people will try to push you to make a decision quickly so you don't have time to check out everything. Take your time, and if they withdraw so be it. You're really better off.
Another tactic used involves offering the item on the lot and having another account neomail you (coincidentally!) looking for the same item that was offered on your lot and voulenteering to pay a hefty sum for it. After you accept, this account will block you leaving you stuck with the inflated item.
Finally, if the offer seems too good to be true, it probably is. Manytimes, they send a neomail saying that they're overbidding on a lot because they need the item for a friend/relative/etc., and you could easily take the time and sell for astronomical amounts of np rather easily. If it really sells for that much, why wouldn't they have sold it in the first place?
Use common sense and be safe everyone.