It's s lot easier to compare new vs. new especially when the optionls are the same. Neighboring dealers normally have nearly equal prices. You can decide on location and reputation- a hundred or so dollars doesn't really make a lot of difference. There is a difference between pricing for new vs. used. So, when it comes to making offers, there is considerably more leeway in used cars than with new. With used cars, there is no set wholesale/retail formula. A dealer can take in a trade for less than value, for example.
I've been scratching my head trying to think of a few things that might be helpful to keep in mind. Here's a few:
Try to get a good estimate for the value of your trade in before you go shopping. Clean the car and remove all your favorite junk. It might make you a few extra dollars and it will serve to assure the salesperson that you are serious about a deal. You could save $1000 on the price of a new car and receive $1500 less than your trade is worth. You wouldn't be the first.
For a new car:
Research the car you want with the prices of factory and/or dealer installed options. Check ads for the dealer to get an idea of the options available in their stock. It can get really confusing when the dealer inventory is considerably different from what you expect. Remember that the manufacturer's suggested price includes dealer prep
. But some dealer addons, like trailer hitches may have unpublished value.
Also, a dealer may advertise selling a car for invoice, or $100 over invoice. They will even show you the invoice. But dealer's get spiffs and rebates from the factory. So a $20,000 invoice may give considerably more profit than just $100. Also, don't forget they can build profit on your trade.
The store finance manager can build gross profit by directing you to their partnered financial institution. It's best to talk to your own banker before you sit at his desk.
The same considerations for trades and financing apply, plus:
There is no set wholesale/retail formula. Blue book is only a guide. Commissions are based primarily on a %age of the gross store profit. If a dealer has taken in a trade at under value, or if they allow less than value for your trade, they create profit on the wholesale end. If they sell for over value, sell you addons, and use their partnered finance institution they make profit on the retail end.
There are a lot of reputable dealers, more than there are flakes. Unfortunately the flakes give the business a bad name. Ask your friends and relatives if they have dealers they recommend.
And, you can't offend them with a low low priced offer, if you really are serious about buying.