The main issue is that a buyer can file a chargeback through Paypal after receiving the domain. In that case, they just yank the funds out of your balance unexpectedly. There's a time limit on resolving such disputes, and dishonest people will string a seller along until the opportunity to file a dispute has elapsed.
Trust isn't the only issue. I had a guy file a charge back by accident because – months down the road – he didn't recognize the transaction and assumed it was fraudulent. He wasn't trying to cheat me. But he didn't refund me on time either. So the deadline for filing an official response with Paypal came and went while this guy kept telling me he'd resolve things. He admitted his mistake and ultimately repaid me. But the charge back itself was automatically decided in his favor even though he admitted it was erroneous and completely his fault. Huge pain in the neck dealing with him and Paypal. Having my balance suddenly drop without warning wasn't fun either.
Paypal itself is fine. But ask yourself how inconvenient it would be if the transaction amount were deducted from your balance or bank account one day down the road. If the amount is large enough to cause a problem, then don't use "naked" Paypal. Instead, use an escrow service. Clothing a Paypal transaction with Escrow.com means that Escrow.com deals with Paypal charge backs, if and when they occur. You just get the money and are done.