OKAY, HERE'S THE DEAL ON THE EXPLOIT:
Earlier today I tried using 2 PS3 Rock Revolutions and a 360 Beatles Rockband and it didn't work.
After work I went back and took two seperate stacks of games to the registers and here's how things have to work. You CANNOT have 2 of the same UPCs on the transaction. At least not RR on PS3 because this time I gave him a 360 RR, Beatles Rockband, and then a PS3 RR. I was very upfront in telling him how they needed to be scanned and it worked like a charm. He said "You just got a $60 game for free" and I said yeah anyone can do it and he was blown away.
Now the next stack didn't go so well. I had another PS3 RR, FIFA 10, and NFL Tour. Now the NFL Tour had a tag saying $19.99 but had a handwritten "9.99" over it. Well it initially zeroed out FIFA 10 but I was being charged $25 total. When I pointed out that the NFL Tour should be $9.99, he changed it but then when he re-totaled it I was getting RR for free. I then had to go find a $9.99 that actually rings up that way so NO MODIFICATIONS can be made on any prices manually or it will zero out the cheapest one.
I swear it was my lucky day. It was a new hire wearing a white shirt and he was totally down with it. My friend came in and met me there and he did it twice as well with the same guy.
Simply brilliant.
I think I mentioned earlier that I have a personal vendetta against Best Buy for a very good reason so my conscious is crystal clear.