check if the
tranny is hard to shift (if it is a 5 speed). T5's are not good if abused... they can't handle powershifts. So that would be a sign of abuse. Pretty much if the car was taken care of (regular maintenance, tune ups, etc etc.) then it should be a good car. Look for leaks around the oil pan and valve covers, and between the oilpan and the
tranny (worn rear main seal=
tranny has to come out to replace it). If you can, look at the condition of the plugs, wires, air filter and such. That should give you an idea of how well it was taken care of... even though they could change them just to sell the car. Also, if you know a good mechanic/shop have them run a compression test. How's the interior? How's the weatherstripping? Do the windows go up/down easily? Do the power mirrors work? (It's common for these to go bad). Are the tires worn? How is the spare tire and are the jack/tools there also? When you go on a road test make sure you turn off the radio and try to listen for any worn wheel bearings or any abnormal noises. Good luck!
Edit: sorry, I didn't see the last part of your post. So it's an automatic.
general questions about 5.0 mustang please help !! 
