I need advice and tips on finding a used car and not get ripped off.?

Some of you may have read some of my other questions concerning my car that is no longer operable. I am now having to take what little money I have as a down payment and buy a new, well used car. I don't have great credit, really none at all, I work for myself for cash..been doing it for a number of years, so I have regular steady good paying work. So, I'm kind of in a pickle. I have no choice but to go to a "Buy here pay here" lot and get a car. Yes, I know they are overpriced and all that, but I have to have a car and don't have a co-signer and that's just all there is to it. I need a car and I need it now. I don't have a ride to work after last week, so I'm screwed without a car. I need tips on what to look for in a crooked used car dealer/person..how to not get bent over and buy a car that will need work tomorrow for more than it's worth if you know what I mean. How to talk to the dealer and get him to work with me and bargain? What advice can anyone give me? Not looking for anything fancy, but not looking for a lemon either. Must be a reliable car..that's my #1 priority. Can you help?