Can anyone explain me, what is the main difference between E-Commerce provided by Yahoo and open source E-Commerce like PrestaShop or OpenCart? What is the best solution for small size eshop ? Any good/bad experiences with any of those ? Any S.E.O. problems with this kind of open software ?
I would avoid Yahoo at almost all costs. They take a huge % of your revenue as well as fixed monthly fees. If you want an all-in-one setup, I would go with Volusion or one of the other companies with more reasonable fees and better support. Oscommerce and Magento are other very well supported carts that are completely free.