Can You Use a Shopping Cart Link on Ebay

no - it would be against ebays TOS
However I have run classified ads that contained links to my website that had my Fantasos payment links on it (actually it was a free product - I gave away the 100% off coupon code on my ebay page)

I was running an experiment on the effectiveness of their classified ads. I ran it during Halloween shopping and the traffic to it was dismal.
I got 100x more traffic to my "baby" website (it was less than 3 weeks old) then I did from my Ebay classified page.

Because it was an experiment I would post the results on the classified page and when I changed my title to include the words "ebay sucks" my traffic spiked. They were finding me through the search term ebay sucks but they weren't finding me through Halloween Costumes which is what I was striving for.

I did recieve a ton of email from other frustrated ebay sellers who liked what I was doing.

My classified ad didn't make me any money and only gave away less than 5 craft ebooks. My organic traffic was what earned me the money and that was from a website that was less than 3 weeks old (I was late getting it built because of some server/software incompatiblity issues)

Depending on the product - my "love" for Ebay has diminished significantly.

You can always use the "about me" page to build your list. Put your optin form right on the page - thats allowed.