Looks very definitely a typo for avviamento. The seller will receive the gain on the goodwill, the difference between the sales price and the book value.

--------------------------------------------------
Note added at 52 mins (2010-11-02 07:55:35 GMT)
--------------------------------------------------

I appreciate your points. I only really looked at the second instance of the term.
The definition you give, which obviously demonstrates the existence of the term, just doesn't seem to fit the second of these two contexts. You can't have a gain on a loan from the sale of an asset, but you can very definitely have a gain on the sale of an asset, which is goodwill. If the first instance is correct, that the purchaser will have to pay the stamp duty on the "avvitamento" understood as the loan to repay current interest charges then this may well not be a typo.
However, I can never remember seeing the term, although it does ring a faint bell. I doubt you will find a specific term for it. Only a very stupid bank is going to lend to a firm to enable to pay interest on an existing loan. It is "throwing good money after bad" as they say. Governments might do it to save jobs.

If you want a translation of avvitamento this is what I would suggest.

However, it might be worth checking with your client becuase it doesn't make much sense here.