[carguychris]

Most states' laws do not specify what are considered reasonable measures to ensure the firearm is not sold to a prohibited person. Most states (if not all) have laws mirroring Federal law, which say that you cannot KNOWINGLY or REASONABLY SUSPECT that the buyer is prohibited. So, basically, ask for a ID to verify state residence (in your case, Florida), verify minimum age (in your case, 18)...

This is basically what I meant, NavyLT gives more detail. Most states that allow person-to-person sales are fairly vague about what exactly the seller has to do to verify whether the buyer is eligible.

For instance, here's what the TX Penal Code says about it.

Sec. 46.06. UNLAWFUL TRANSFER OF CERTAIN WEAPONS. (a) A person commits an offense if the person:

(1) sells, rents, leases, loans, or gives a handgun to any person knowing that the person to whom the handgun is to be delivered intends to use it unlawfully or in the commission of an unlawful act;

(2) intentionally or knowingly sells, rents, leases, or gives or offers to sell, rent, lease, or give to any child younger than 18 years any firearm, club, or illegal knife;

(3) intentionally, knowingly, or recklessly sells a firearm or ammunition for a firearm to any person who is intoxicated;

(4) knowingly sells a firearm or ammunition for a firearm to any person who has been convicted of a felony before the fifth anniversary of the later of the following dates:

(A) the person's release from confinement following conviction of the felony; or

(B) the person's release from supervision under community supervision, parole, or mandatory supervision following conviction of the felony;

(5) sells, rents, leases, loans, or gives a handgun to any person knowing that an active protective order is directed to the person to whom the handgun is to be delivered; or

(6) knowingly purchases, rents, leases, or receives as a loan or gift from another a handgun while an active protective order is directed to the actor.

The key words in all of these regulations are "intentionally" and "knowingly". If the seller didn't intentionally or knowingly sell it to an ineligible person, the seller is theoretically in the clear.

That said, I'm still not personally comfortable selling to a stranger whose identity I can't verify by looking at their photo ID to verify that they're over 18.