I write up my own bill of sale (templates online) for both parties to sign and have a copy - just to help cover my ass (and the buyers). i.e. vehicle sold as-is, odometer is true, free of liens, etc.
Cash/counterfeit pen...or cashiers check AT the issuing bank.
I've sold a couple cars to Ags through TexAgs. I should have...but didn't bother with the plates. Get the car off your EZ tag account and make sure you immediately submit that form (VTU-346) which will cover you if they run tolls or go on a crime spree. Which one guy actually did run some tolls on accident, but apologized and took care of it.