But noticed that g11's seem to be so cheap even if avoiding the 2017 tax hikes is there any particular reason? They seem to be cheaper than 3's and 5's
Because the second hand market doesn't care about the big exec class that much, and most punters assume big car = big bills, plus the complexity of new generations means home/indie fixes are getting harder and harder.
They can be utter bargains but you'll want a warranty I think, 4 corner adaptive air suspension can give issues as can some of the cameras (that's from personal experience) but I rate them highly the 740d xdrive is a great package.