First answer: get a contract and a lawyer who is a public notary (he'll give you the contract actually, if you are in SD, I can hook you up with one that's trustable.
In the negotiation you determine who pays for the lawyer, most of the time it's the buyer.
You have to sign the matricula on the back (and the contract ofcourse). He gives you the money, you give him the car and the matricula and that's it. Make sure you get a copy of the notarized contract.
It's his responsibility to go to plan Piloto (check if it's stolen) and some buyers insist to do that together with you, but the last time I sold a vehicle the buyer said he already checked somewhere else (I think he said dgii) that all was fine. Also his responsibility to get the car on his name (and pay the tax), you should insist on that though and check later at dgii if he did, if not you can notify them, with a copy of the contract that the car is not anymore in your possession.
The money can be received with a certified check that you can cash at the bank where it's bought. Don't accept a normal heck. A certified check is paid for and will not bounce.