Weebly offers Google Checkout and PayPal shopping carts, but if you already have another shopping cart, can you use that one instead?
The answer is yes, as per this article in the Weebly support center: Other Shopping Carts. “Any cart will work so long as the vendor allows you to create embeddable product listings / add to cart buttons. Any such embeddable options can be added to you site via our custom html element. “