Anyway I learnt him a lesson the other day
It wasn't an English lesson then?
he was looking at Audi A4 Avant TDI's and I found him a newer, less mileage A6 Avant petrol. And proved he could never recoup the price difference in fuel savings, of which would be completely redundant once the TDI throws up a repair bill
What petrol? If you say 2.0TFSI then no, just no. They are almost as complex as the 4-pot diesels, and have almost as many shortcomings (DPF aside). Mine threw up a £2000 bill.