I'd say D) nice card, let me know if you ever want to sell. would be the most appropriate.
Mainly because even if a card is PC there may always come a time where you need the money
or you want the funds for a higher sought PC card. So it's good to know that there are potential buyers you can contact immediately before you would ever have to post it for sale. Besides D) isn't really making an offer so much as making it known you got a nice card and other people do want it