I've posted this elsewhere, but I guess it bears repeating. I pay cash, which helps a bunch. I shopped my GT1 AWD at three dealers, armed with knowledge of dealer cost (sort-of) and trade-in value of my current ride. Spec'd the car out myself (simple - HiChroma Red, GT1, AWD, Driver Assistance package) and handed the dealers the spec sheet along with my contact information. I asked for a simple bid/quotation, one chance, no dickering, net cash price FOB dealer's front door. I let them inspect my trade-in if they choose, and I walk. Call me tomorrow with your best price.
So I know some things. One is that for the GT's, the dealer invoice cost is about $3,000 below MSRP, not counting all the other hidden things customers never see like dealer incentives, quota allowances, etc. The other is that my trade-in is in the $6,800-8,300 range. Both numbers from Kelly Blue book.
Because I spec'd the car out, there is nothing any salesman can do for me. I don't need a salesman. If you can get directly to the sales manager, you still pay a middleman commission (lousy #@$% system, but it's traditional). So what is a fair profit for a dealer to spend 15 minutes entering an order into their computer? A couple thousand on the Stinger keeps the lights on and pays the hired help for doing much of nothing, plus a couple $thousand on the trade-in sale.
But there's more to consider. The winning dealer gets some free advertising -- from me. The losing dealers get the same advertising on how far off my price was, and that can be an intangible loss of more than a few thousand dollars considering other buyers they now stand to lose. We're talking potentially a bit of volume and thousands in profit. No car is worth MSRP or over, IMHO.
The only downside is that you have to wait for the car. But you do get better quotes. There was $2,500 difference between the low and high bid on my GT1 AWD. I took the low bid, even though that dealer is 55 miles away from me.