Not sure if BMW and MB are the only cars your friend is interested in checking out, but if $25K is the price range, one car I just recently bought was a used 2015 Lexus IS 350 with the f package. My friend's daughter was selling her car and I have to admit, it is a pretty fun car to drive! Gas mileage isn't he greatest at 27-29mpg (highway), but the car drives amazingly well. It has 19" wheels and has a factory suspension kit that makes it corner as well, if not better, than my old 90 BMW 535i! The car had 38k miles on it when I purchased it for $20K! Something to consider!
Of course, with any used car YMMV!
Good Luck!