In general you're better selling on the open market and skipping a trade in. This market has kind of flipped things around, at least in the automotive end of things.
I recently traded my truck for a new one and got a ridiculous amount for it. More than what I paid for it.
I haven't been in the market to trade a tractor in many years, but assuming the OP's tractor is in very good condition I'd say he's being low balled. Yes, the dealer is in business to turn a profit. But no, the week's or the month's profit doesn't have to all come from one customer.