I used one method for every car I've purchased since 2005 (three). Most of the time I spent was obtaining emails for 10+ car dealers. I then sent the same email to each of them, essentially worded as follows:

"Dear ___ I will be purchasing a black model ___ (with the following details) ___ for cash this Saturday. No trade-in. I am sending this email to 10 dealerships. I will reply to one and only one responding email. Your email must expressly state that your quoted price "includes 100% of the money I will have to pay including taxes, registration, plate costs and every other fee".

I will not consider any email that arrives after 6:00PM Friday.

Thank you, _______

I have never received fewer than 6 offers. Most were very close in price. I did not always accept the lowest offer due to issues such as distance, out-of-state, and spirit of the emailed response. This has been so successful that I will never buy a car again without following this scenario.