It's stupid to say that they're ne seller club. They have to buy players and sell others.....
The point is IMO that they don't sell their in-form players to win money. That's a good thing as selling Sheva would be a stupid thing to do right now.
On the other hand, they could get huge money by selling Sheva, and then easily afford, let's say Robinho, Cavenaghi, Gilardino, Cassano (at least 2 of the mentioned).
Juve is a seller (didn't we sell Baggio, Zidane, Inzaghi,....) and a buyer (Emo, Thuram, Nedved, Buffon,.........)
Moggi is good in balancing both needs and I trust him on that.