I just sold my copy of CS2 for 300 euros. it was unregistered but used. I mailed Adobe Piracy to obtain an email saying that the serial number I have on the CD is in fact unregistered and valid.
With this included the copy sold instantly. I am a bit skeptical of a lot of vendors of software on ebay. the buyer of my copy told me that he bought a copy of ebay and it was a trail CD (factory sealed) with a inkjet printed scribbled serial number on a note with it. Needless to say, the serial was not verified by Adobe.
I would be very careful in buying used or packages that i cannot see of software to be honest...