You could be the target of a fake buyer. You advertise a product online on an auction site or similar and receive an offer from another user of the site. They are extremely interested in the goods. They are the winning offer and during the negotiations by email you receive a message from ‘PayPal’ or a similar service stating that the purchaser has lodged the required payment. You are asked to confirm you have sent the product but you soon realise the email is forged. PayPal never confirm payment by email.