I was well under invoice on my last vehicle purchase. It was a built to order, so I placed a few "want ads" online through local dealerships. First one that responded with a close to invoice I emailed back with a real low ball offer. They responded with a decent price. Back and forth again and a great price.
Never mentioned a trade and was never asked.
2 months later and my Jeep arrives. While signing the paper work, I ask if they want to "buy my old Jeep". After a good 30-45 minutes of them looking it over they come back and give me a price. Same price that CarMax had given me the weekend before and the 14 day guarantee price nicely printed out on a piece of paper.
Do you know how easy it is to scan something, manipulate a few numbers and reprint it?
"That number is a little low", pull out folded piece of paper. "This is what I was offered last week." My sale to the dealer went up, a bunch!