If the parents are big MB fans it means that they are more than of average means, i.e., they have some money. The daughter is gone and they have more cars than they need. This means that, one, they probably really don't need the money from the sale of the sl. Two, they need the room in the garage. Three, they don't need the insurance costs. Four, depending on how they felt about the daughter, they may not want the car around as a reminder.
And five, the car has relative high miles on it.

Read all the above as an opportunity to get a really good deal on the car. Start out at $7200 and sing a song about possible repairs, i.e., timing chain, transmission, shocks, etc., etc. You've looked into the history of these cars and they can have a lot of costly repairs at this age. Also, the job market is not too good at the moment and your company is looking a bit shakey. Yada, yada, yada.

Let them drive you up to about $7,800, but make them work for it. Start digging your heals in at $8,000 and I'll bet you can get it. Don't be afraid to walk away and come back later. Don't convince yourself that you have to have this one. There are literally thousands of these sl's on the net.

I say all this because I lived in the Middle East for 10 years and delt with Arab business men on a daily basis and you haven't done business until you have done it with an Arab.

I bought my slc off the net and saved 20% in about 5 minutes of bargining. The seller was divorced, had a girlfriend, but most importantly, had two kids starting college next semester. And, as with your car, needed the room in his garage.

Good luck