Be careful if you plan to bid for Photoshop on Ebay. I won a bid for PS7 and it installed just fine using the serial nbr provided. I then called Adobe at 1-800-833-6687 to verify its status and was told that it was not a valid number. It appears that the software can be altered to accept an invalid serial number and if you don't call Adobe you never know you have an illegal copy.
Since this occured I have been emailing the seller before I bid asking if they have verified the registration status of the item. I have found that after sending this message I am blocked from bidding on the item. Appearently if the seller knows that you are going to verify registration status with Adobe and the item is actually already registered or the number is invalid he just blocks your bid and saves himself the hastle of having to refund.