if you want to know about transfers...
I AM NOT AN EXPERT, you experts feel free to correct me, but I see you are here in TX. You can sell face to face in TX to another TX resident of age and with no issues on owning firearms, people prefer selling in TX, handguns at least, to someone with a TX CHL. I'd do a "bill of sale" and get their drivers license info .
Other than you and your buyer being in TX, all modern firearms must by law be transferred from a Federally Licensed dealer. In most cases, you can ship firearms directly to a FFL holder for subsequent transfer....handguns would have to go FedEx or other overnight, you can mail a rifle/shotgun by USPS. You'll want to have a signed in ink "original copy" of the FFL that it is going to. Not a fax. You might be told that you don't HAVE to have the copy, just the information that they are an FFL and reasonable proof that it is correct information but I'd want a copy of the FFL as the shipper may ask to see it. FedEx wants the handgun taken apart. On your first time deal out of state I'd go to an FFL and pay their fee, likely $10 to $25 and shipping depending on the dealer, to have them do a transfer. Most can ship 2nd day so the cost is about the same. Most auction sites list FFL's who do transfers. You will likely pass all or part of this shipping cost to the buyer. If you are in DFW, I'd recommend Sportingarms.com .