I just traded in 12 games the other day. They weren't really in-demand games, so the trade without the bonus would have been like 33 bucks [!]. With bonus, 78. Not too bad, I paid about 100 for them all, so 22$ is less than 4 rentals from BB. But some of the games i traded in, they're selling for 5.99-9.99, so that's not too much markup.
At first he had me getting 40 bucks extra credit, but then I said 'can you ring them up as 3 sets of 4' thus getting me 45 dollars credit. After a minute of thinking, he did.
And on mine receipt also, each game had a bonus added to it, and it wasn't broken down as to original value/bonus value.