Q: I placed an order over the internet. When I click "confirm", is the transaction binding?

A: According to almost all poskim, such transactions are binding based on the concept of situmta. The Gemara (B.M. 74a) teaches that the wine merchants would often make a sign on wine barrels that had been sold as an indication that they were sold. If the common business practice is to consider the sale binding on the basis of this marking – even if no other kinyan was made – then the sale is binding. The poskim extend this idea to any common business practice, minhag hasocharim, as a binding form of kinyan (C.M. 201:1-2). Thus, if the common business practice is to consider internet transactions as binding when the customer clicks on the "confirm" button, this action is also given halachic validity as a modern form of situmta. Other possible examples of situmta include affixing a signature on an order form and "mazel and bracha" in the diamond business. Many poskim even suggest that cash payment does finalize transactions based on situmta nowadays, since that is the common business practice these days.