This is primarily about what's known as "first-sale doctrine". Basically, if the copyright owner gives you a legitimate copy of a work, you are free to pass on

This is primarily about what's known as "first-sale doctrine". Basically, if the copyright owner gives you a legitimate copy of a work, you are free to pass on or resell that particular copy without needing to ask permission from the copyright owner. So no, you're not allowed to make copies of the disks and sell them, but if you buy a stack of 50 promo disks second-hand, you can resell all 50 of them. I'm not sure how it works with purely digital goods, but presumably (IANAL) you'd be in the clear if you deleted "your" copy when you passed it on to someone else.