im looking at buying an Audi s4 b8 model, I was wondering what the maximum mileage that is still healthy would be ? also things to avoid when buying one of these models 

any information would be greatly appreciated , thanks 

Definitely have a look at YouTube buyers guides. I believe these engine have a timing chain. And not all garages want to work on them when this job is needed. Always check service history as it shouldn't be skimpt on.