i've found below average miels cars to be troublesome, i'm weary of modern diesels there not as long lived as everyone thinks, then engines do ok but everything around them, turbo, dpf, egr will fail but if i see all the OMFG bills in the service history i'll buy it anyway.
a lot depends on who it's been driven as well. a car that has been driven hard from day one is a good buy if it's been maintaned as your not going to get meany age related fails asa all the wearing bits will be new ish, buy a low miles car and drive it hard they tend to fall apart