Sell a laptop online. Is it correct that the buyer can theoretically withdraw the transfer after he has received my laptop by mail?
A transfer can't be withdrawn if it is booked. And that's the case no later than the beginning of the next working day.
If you have not described the device sufficiently, or want to cheer him a broken thing, of course, he can demand his money back
A transfer can only be withdrawn as long as the transfer amount has not yet been credited to the recipient account.
When using Paypal, a buyer with intent to cheat may open a "case" within a certain period of time and then demand his money back, citing certain reasons.
Therefore, high-quality goods should be sent even in private sale only with the option to track shipment with confirmation of delivery, as well as sufficient shipment insurance. In addition, carefully document the entire packaging process and the delivery of the consignment and, if necessary, include a witness.
If possible, clarify in advance with potential carriers, whether a binding handover agreement (handover only to consignee personally with ID) is compatible.