You don't do many deals correct? Signing a message is a proof that he is serious, and the escrow does not protect the seller. If you know how it can protect me by giving to a person the email and the password and he changes it and say it is not correct. what can I do in that case?
I have done deals before. Have BTC is an address means nothing If one is dishonest and has an intention of scamming you. The best sign of commitment is using an escrow.
The escrow will help mediate the transaction and dispute. Should the other party start playing games and claim that the password is incorrect after changing it. The money still gets sent to you once the dispute is resolved. That's why you always have to choose trusted escrow services.