If he is that serious about the quality of the car he won't mind you having a mechanic check it out. It can be well worth the 100 to 150 to have a professional do a thorough check out of the vehicle.
Look for blowby/compression issues and the other usual things like front end problems, signs of rust, etc...
Good luck.

You can check the shop recommendation forum here to see if there is anyone in Orlando that has a good review.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique