The dealer I'm working with personally locked my rebate. If it goes down, they will still honor it. if it goes up, it goes up and they will give the higher rate.
One thing I've learned over the years is make them honor what they say, if they dont they wasted their time because I will walk. No one likes to waste their time (salesmen or me) and I constantly reinforce what they had said.
I already walked on one local dealer who thought he could pretty much force a sale at a price he wanted (when he wouldn't show me the invoice for xplan it was walk time). I've walked out of buying several cars from them. Their favorite tactic is to get all your info for the finance department, even if your only looking. They don't need anything but your name and phone number until you decide what your going to do (ford will be getting a nice note about said dealer, I'm sure they will be interested). Not to mention this place will call you 2-3 times a day, basically bird dogging you.
I'm the type that if there is something I want I'll hunt it down (the salesman I'm working with is pretty damn savvy too) until I find it. Trust me, it's found ;), in one place or another.
If I ask for something in specific such as a 2012 v6 mustang... don't friggin try to sell me a $37k v8 mustang I don't want... you lose my business.
I'm pretty easy to get along with as long as a salesman doesn't try to blow sunshine up my butt and is willing to work with me, I'll gladly reciprocate.