Something those not familiar with the actual process need to know is that the term "Online gun sales" does NOT mean you can get on the Internet and order a gun delivered to your door.
Anybody in the nation can ADVERTIZE a gun for sale on the Internet. Once a buyer expresses interest, there are essentially two ways to go about it: Payment can be arranged for out-of-area transactions (credit card, check, MO) & the seller then ships the gun. Or, if close enough, a face-to-face meeting's arranged, and the money & gun are exchanged in person, pretty much like you'd buy anything else locally in a private party purchase.
In the Internet transaction case, there are federal (and in California, local) laws that dictate how the mechanics work. You don't just drop a gun in the mail & call it good.
Shipping from state to state requires the gun be sent to a federally licensed dealer in the buyer's state to be transferred to the buyer, which involves the background check & paper trail.
A sale from a seller here in Utah to an out-of-state buyer who's close enough to arrange a face-to-face transaction similarly requires, by federal law, dealer involvement in the buyer's home state. You don't LEGALLY wander over to Montana, buy a gun there, and bring it back home. Montanans don't LEGALLY take a leisurely afternoon drive to Utah, buy a gun, take possession, and drive leisurely back home with it.
KSL provides ad space for gun sellers, but it has no obligation to enforce federal law in subsequent sales, those involved in the transactions are responsible for following all applicable laws & regulations.
There are NO laws in Utah that prohibit face-to-face sales among Utah residents who are not otherwise prohibited from ownership, and NO laws in Utah that require background checks on such sales.
The mere fact that the online ads are accessible beyond Utah's borders does not mean KSL is doing anything illegal, immoral, or fattening.