Used car lot sales - what to offer?
Find the true value first, by going to KBB.com, and use that as a guide.
If the KBB value is less than or equal to the asking price (10,400) then there's no good reason to ask for less. You could try... but you might come off bad. If you find something wrong with the car that they didn't know about, then you have a real reason to ask for less.
The best way to get a lower price is to shop around. Contact other dealers in your area, and ask them if they can beat that price. Make sure you give them all the details too (2004 mustang, 3.8 six...). If you're potentially buying a car from them, it's well-worth it for them to play along. But don't let them talk you into anything you don't want.