I gave a deposit once for a car, that was a big mistake. Took me a month to get it back. I gave him a check and he said he wouldn't cash it. The next day I called and told him I had a better deal send me my check. Oh we cashed it.
Besides, the last thing you want to do is look excited. Like posted above, go in, look around, be totally dissatisfied with what's there (wrong color, too big, too small, wrong tires, terrible chrome) make him an offer way too low and walk out. Call in a week or 2 and see if it's still there. Meantime, tell the wife to get in back and stop screaming.
I did this once cause I wasn't ready to buy a car, still shopping. They said ok to my lowest offer cause I was walking. I still wish I'd found out what their next pitch was.
The moral to this story is... as long as you have the money, you have the advantage. Give them even a little bit, and they got you. And don't give them your license either! For some reason, they like to hold it while they're talking to you.