I know some people would argue my tactic and say you will only get the best deal if you sit in there and allow the sales guy to keep "going back to my manager to check" bs. They would argue that you are not showing your intent to buy and thus wont take it seriously enough to put together a good offer. And I have found this to be true, at certain dealerships. But those are the dealerships you dont want to waste your time at anyways. Its always funny when they call back and say, Ok we got your email, stating the exact stock # of the vehicle you are interested, now why dont you come in and we can talk about exactly what you want ? Hahah I just gave you the effing STOCK #, thats what I want !! No need for the time suck, buddy.
For instance, I worked in this manner with a dealership in Charlotte. We verbally agreed to my target price, all was looking perfect. Then they said OK just come in here and we can finalize all this. I told them we already finalized all this, send me the paperwork via email, I will look it over, sign, and return it via email then come pick up my new vehicle. They stammered on this, kept saying we cant just email the paperwork, its a federal document and we use hillarys email server ... ect ... ect ... ect ... bs. Just come in here, we will "work it all out when you get here". Red flag. Finally, they sent over the paperwork after a few more calls, now from the sales manager himself. He took the liberty of adding in $500 for wheel locks (really? wheel locks are $30). $495 for tint (I dont want tint, I prefer NOT to be harassed by the cops), and $995 for some other misc dealer prep. So my target price just got blown up by +$2K. Had I not insisted on the paperwork 1st via email, I'd of just wasted about 10 hours driving back/forth from Atlanta-Charlotte. See, these guys are slimy be careful how you handle them.
Heres another thing I learned - get the web url / stock # of the vehicle you want and send that out to as many dealerships as you want. They all work with 1 another and can basically get any vehicle anywhere, and often do trades between their inventory. So dont think hitting a brick wall at the dealer your stock # is sitting at means another dealer cant it for you for less. Case and point - I just bought a 2016 JGC overland. It was sitting at a dealership in TN (Im in Atlanta). I negotiated with the dealer (Rocky Top) for about 2 weeks, we got down to a price they would not budge on. They also needed me to make the 6 hrs round trip to get it. So I called Ed Voyles in Marietta (about 15 min from my house). Told them about the vehicle, and viola, they found an extra $500 off, AND went and picked it up for me. They said they did an internal "trade" with that dealer and were able to get it. Was sorta funny when the sales advisor from the TN dealer called me back to tell me "sorry, the vehicle has been sold you shouldnt of waited" to which I responded, "I know, Im the 1 who bought it, you should of lowered your asking price and delivered it!". That deal could of only been worked through another dealer who could trade them something, so just saying keep that option open.
But the #1 mistake in my opinion is to actually go sit in the snake pit and talk $ with those guys. All you are in there for is to test drive, decide on options, and colors, then GTFO as quickly as possible and start your internet hunt.