A couple of years ago, i had a friend who had a friend.....who imported stuff from China. He brought over some Ping and Callaway clubs that were apparently authentic, but they were production over runs. I bought a brand new, complete set of Ping G2's with a bag for $400(no serial numbers though). They were pretty popular and the guy sold quite a few sets. The first thing I noticed was there were black inserts on the back of the irons that fell out almost immediately. They still worked OK for about 50 games and then the head of the 3 wood flew off, shortly after that face of the driver caved in. Not long after most irons are rusted out on the bottom of the shaft.
So really, I pretty much knew they were knockoffs after about a week, but, I used them for probably almost 2 seasons. For $400 it was worth it, and I liked them so much I actually went and bought a set of real Ping G5's.
I've since heard various stories of production over runs, distributors going out of business etc, but if it seems to good to be true, it probably is. But like I said, for $400, I think I got my moneys worth from them.
Here is a really good warning on Ebay about Callaways.
Check out the NINE WAYS TO AVOID BEING FOOLED BY COUNTERFEITS: part