2008 Mercedes S550 with 150,000 miles
Would you buy a 2008 Mercedes S550 in excellent
condition if the price was good but it had 150,000
miles on it. How many more years or mileage can I
expect to get
This all depends on condition and on how well it was maintained. Since maintenance and repairs on this car are astronomical most cars are neglected and become a money pit. If the car checks out and you can get a copy of the maintenance records and have the money for repairs you should go for it.
How long it lasts will be up to you. If you drive a lot and neglect it, it may be dead in less than a year. If you drive 5,000 miles a year and take really good care of it, the car might last another 10 years or more.
I had a coworker who bought a similar Mercedes. He was in love with the car and took care of it like it was solid gold. He ended up spending his life savings keeping the car going but it was a cool car!
As the owner of 2 SL550's - I can agree with F_O_R. Easy and steady driving along with normal maintenance - these could last forever. Clearly the last owner(s) did not let their car sit. But you have no way of knowing how they drove it. Unless you can get records of the brakes being serviced, Transmission flushed (VERY important), even if the Hard Top motors or suspension bags have ever been serviced. Just to name a few. I think I would probably pass on this one because there are just to many unknowns that could cost WAY more than you ever paid for he car. After 2 SL's, I would not have anything else - but find something newer with less miles.