It is supposed that seller will have several different options. To stand as a grantor and securer of payment Market Space will have to have delivery status to be one of the smart contract conditions, meaning that payment will be received by the merchant only after the goods are delivered. Your thinking here: "A seller get money after a delivery of a product to a buyer or somehow else?" will only become reality after we manage the logistics part to comply with the above comment.

BTW if we speak of digital services/products, here transaction hold won't be necessary due to immediate delivery.

Also what we have to remember is a fact that buyer/seller rating will generally bring additional trust to every deal and decrease the level of mutual doubt for the parties.