While I do make it clear that prints are for sale from my web site, I haven't attached a shopping cart or prices to any image. Even so, I still manage to sell 3 or 4 a year from direct contact over the internet. I would not try to make a business plan based on web sales though - people prefer to see them in the flesh (my physical gallery has been open for less than a year and I've sold nearly 350 prints [framed and unframed] directly to people that way.) The print sales from the internet have paid for the internet site rent, but not much more.
(www.scenebyhird.com if you're interested)