Well the other guys here have good points. The mechanis might be just as negleted as the outside dents, or they might not want to spend on fixing it. How old are those dents?
Also my father sometimes does work for friends or clients and he always gives them a detailed invoice, because nobody, even friends, will believe where all the $$$ go into. Perhaps you could call the mechanic and ask him to show you the invoices where he bought the parts, if he tell you they are in the trash. Then if he bought them at the dealer the dealer has a copy of this invoices.
The antenas do make some noise, as long as the motor works you are OK. The antena mast is the one that usually gets stuck half way, and a new one is like $30.
Do the AC vents work properly when you change the settings in the climate control swithboard? those servos are another 1.5K worth of work is not done at the same time as the evaporator. If they changed the evaporator (as the say)the mechanic should have suggested they changed them too.
Look for scratches or any indication that the instrument cluster has been removed or disasembled. Watcha for wear (steering wheel, seats, springs) that is not consistent with the mileage, like you point out in the steering wheel.
Paying $200 for a mechanics inspection can be a good thing too. By having the seller present, you can show them in their face what needs to be fixed, and you can use this as a barganing point. Also get a carfax report.
$7K is not that bad for a 300E, if nothing serious needs fixing the price is ok. I usually commpare the prices in NADA, Edmunds and KBB to the ones on the paper and come up with a fair idea of current local prices.
good luck
