Agreed. Marketing assessment? That's a gimmick add-in. Tell them it'll cost 'em a sale if they don't take that off.
Story time: I negotiated for a friend who was buying a new Sentra. She didn't know the "Market Adjusted Value" was also complete BS. I told the sales guy that they were not going to get the $1,000 they claimed it was worth over MSRP. And then I raked into them even more because of the attempt to rape the general public over a
SENTRA.
I think you should hold that over their heads. For every minute they argue over that $340, knock $340 off your offer.