I too have been down this path many times. Over the years I have settled on a no BS approach.
* If I am just looking I tell them that. I do not want waste their time.
* Never buy on the first trip. A day or two of thought clears the head. It reduces a lot of buyers remorse.
* If you miss a fantastic deal, it will most likely be there tomorrow.
* I do not care what the service charge, prep. charge, service fee, taxes & etc. are. The only number I want to know is, what I write on the check.
Finally, I make it clear. Tell them three time so they know I am not kidding. I only brought one check! Any other costs they forgot to mention, comes out of their pocket.
Yes, it is hard nosed, but it works. If not, they probably did not need my business.