Repalcing bank 1 turbo on a A6

What is your question?

I want to buy a 2000 Audi A6 has 89,000 miles that is smoking thru the muffler. The guy says he took it to Audi Service and they said that the bank 1 turbo needs to be replaced. How hard of a fix is it and can I just replace the bad one with a used one from the junk yard?