The standard procedure for selling domains is to fully protect your payment with escrow, and only once the payment is escrowed to your satisfaction, you can then safely push the domain to the buyer using the procedure set out by your domain registrar.
Make sure you use an FCA authorised escrow firm, as there are plenty of scam escrow firms out there.
I work for Europe's leading escrow firm Transpact.com (which is FCA authorised), and using our escrow service costs from only £5.98 per transaction.
The key to escrow is ensuring that the escrow conditions you set fully protect you - the escrow conditions set a list of events or triggers, and specify on each who gets the buyer or the seller.
You set the escrow conditions, so ensure that you are certain that you will be able to provide evidence that you have met the triggers specified, so you are then certain to get paid.
There is no standard set of escrow conditions used in the domain sector (which is a shame) - everyone seems to use their own, and they can vary depending on the particular registratar requirements (.com is different from .org which is different from .co.uk).
The whole process can be incredibly quick from start to finish (our quickest domain transaction was 17 minutes from the very start of the sale until the payment was cleared in the seller's bank account), but this does vary with domain registrar requirements.
I know you are selling, so this does not apply to you, but let me add here that when buying there is also the added risk that needs to be borne in mind that the domain being purchased may turn out some time after the sale has completed to have been stolen by the seller - this is extremely rare, but I thought I should mention the possibility. If this were to occur, ownership will depend on the rules of the particular registrar involved (so once again, .com is different from .org, etc.).
