I think you have to host iSell with MacDock, and well, if they won't even answer pre-sale questions, do you really want someone like that as your web host, let alone your businesses web host? You will never be able to move to someone else (you'd have to change shopping cart programs).
There is nothing wrong with commercial solutions, but I'd say at least look for one that gives you a license and will let you host with whatever host you want to.
Being strictly tied into one particular vendor for that much of your ebusiness, in IMO, not really a smart move. At least with licensed applications, you can change web host vendors and take your application(s) with you.