Soum's policy is that when you report a device as different from its listing, Soum investigates; once a mismatch is confirmed, Soum sends the device back to its seller and covers the delivery costs. A device that matches its description, however, can't be refunded once the sale is under way.
Certain listings show the badge “Guaranteed & Inspected by Soum”, offering exchange within 10 days plus an extended warranty of 12 months, so look for it on a device's page before buying. If you pay with Emkan, any exchange or return must happen within 24 hours of delivery.
Source: Soum: policies and terms (return policy)