As well as the options mentioned here (e.g. PayPal + transfer, Escrow.com, Epik, DAN), all of which have benefits as others have outlined, remember that there are also other registrars with marketplaces that can work very well, if the buyer is willing to conclude the sale and keep, at least for 30+ days, the domain name at that registrar. This is not a comprehensive list but Dynadot, Epik, Namecheap, NameSilo, GoDaddy, etc. all have marketplaces.
In many ways I see this as the most secure way for buyer, since they know the transaction is supervised by the entity that controls the registration. Look into the payout conditions, of course, to make sure they are acceptable to the seller.
Sales at registrar marketplaces can also be super fast. I have had first contact with a potential buyers, agree on price and after giving them several options they select the registrar marketplace, I set the price for BIN there and send them link to marketplace listing, they bought the name, and it is transferred and my account credited (although funds on hold for a period of days) all within one hour.
Not sure if you plan on global sales, probably, but keep in mind that there are countries in which PayPal is not allowed, and many countries in which Escrow.com is not operational, so you really need a third option. As far as I know the main registrar places work everywhere (someone let me know if that is not right).
If the initial contact is directly to me e.g. via my website the preferred option I offer the potential client is always the registrar marketplace, if it is registered at one. I use about 10 registrars, but prefer, other things equal, those with marketplaces for this reason.
Bob