Well last night I opened everything up with my daughter and we sorted and then inventoried everything. It was missing 141 pieces (52 unique), so not too much.
The worst was one of the baseplates being missing. Those aren't cheap from US vendors, unfortunately, and I don't want to wait for one to ship from Europe. It's already all on order on bricklink. If it weren't for one odd item I could have got it in less than 3 orders, but I'm good. The total was about $30 (guessing a little bit due to shipping).
I'm certainly not complaining about the deal! I figured I am minimum $50 ahead on the other sets even without considering the nearly complete pet shop thrown in. The seller was pretty straightforward about the condition. He said it weighed about right, but couldn't say it was actually complete without doing a full inventory, which he understandably didn't want to do at that price.
He seems to specialize in finding sets with major box condition issues, and then passes the savings along on craigslist (I'm sure he's making money, though--good for him). He's a saint if you ask me!