FYI, you don't need an FFL when selling a firearm. You certianly can use one as an intermediary if you wish, but it is not necessary. If you sell to another individual in Texas even if you don't meet in person, you can ship to them. If your shipment crosses state lines it must go to an FFL in the recipient's state before they can take posession of it. You can mail directly to that FFL. It is the buyer's resonsibility to set up that FFL. Have the dealer send you his license #and address and check it against
https://www.atfonline.gov/fflezcheck/. If you sell to another texas resident without an FFL make sure you complete a bill of sale that makes the buyer sign off on the prohibiting questions. Like this one:
texasguntrader.com/billofsale.pdf. If you do and the gun is ever recovered in a crime, you will have the information you need to provide to the ATF that shows you legally sold the gun, and you can attest to the fact that you had "no reason to believe the buyer was a prohibited person".