I love cars and in order to experience them, I buy and sell every other year(used ones) so that I don't have to pay the depreciation. I have a Prius 2 and a ML350 at the moment. Ex owner of Civic, Lexus GX470, Nissan 240SX
Few Tips of buying used cars from my experience :-
1. Buying from pretty well to do folks is good since its dealer serviced most of the time and no skimping on the maintenence and folks who have all the maintenance records( location! location! location !) :)
2. Try not to buy the first car you see unless you have compared it with the other similar models
3. Start and test the car when engine is cold, request this from the owner
4. Never blindly trust car fax since lots of stuff doesn't get reported. So get it to the mechanic or get your car savvy friend to check it for you
5. Drive it on all the gears(stick) and on the freeway. Turn the steering wheel left and right to the maximum and go around, lookout for any squeaky or cracking sound
6. The VIN no sticker should be almost everywhere. The hood, all the doors, the trunk, if its missing then possible body work has been done and possible accident
7. Usually German cars are more expensive to maintain so try to get as much as remaining warranty possible without paying extra for it.
8. Check the spot where the car is parked, there should not be any oil marks/trace.
9. Compare the market value of the car (kbb.com) and also overall price of sellers willing to let go
10. Pet Hair - It costs almost $100 to $150 to remove them by the detailing shop so include this in your negotiation
Car service tip :-
1. When you need to repair your car compare it with private mechanics and also dealer with the coupon rate. Most dealers honor coupons from other dealers around 50 mile radius. ML350 private mechanic charges $120 for oil change and I found a dealer coupon for $88 and of course dealers always preferable if price is the same
Good Luck!