You need to find out more about this vehicle. As they say, if it sounds to good to be true, it probably is. Also, how important is a warranty to you? How many miles per year do you plan on driving? You should try to find out how this dealer came of the vehicle. If they bought it from an auction, then this vehicle went really cheap and that could be for a reason.

If it has the original battery, it will most likely need to be replaced. You need to determine if the N63 campaign has be performed on it. You need to check the iDrive system to see what maintenance is due or going to be due; all though someone could clear them so it looks like the service was done. A PPI would help determine that though. What could be due in the near future, brakes. The 50i is also a thirsty engine, I don't know how it compares to your 2001 since you didn't list which engine.