Buying Mac software (QuarkXPress) on eBay—things I need to know first?

I hate Quark, but I need it (version 6.5). Paying full price for it seems like a fool’s errand. I see several listings on eBay, and I know enough that:

  1. I don’t want an academic version (I’m not a student/teacher and don’t want to be asked to prove it if I did attempt to buy)

  2. I don’t want anything that’s listed as OEM, NFR, Dealer Demo, Promotional

  3. I need an unregistered copy, and not a registration transfer. Is it true that registration transfers exclude you from being able to upgrade? (although I hope to God I’ll never need to upgrade)

Is there anything else I should be taking into consideration before buying (aside from the basics: check out seller history, don’t pay by cash transfer, look out for scams, etc)?