(in the US) No, it is perfectly legal. However, depending on where you are, there may be stipulations. In most U.S. states, you can sell privately owned firearms to anyone that can legally own the firearm in question with no paperwork required, however, a few states require the sale to be processed as a transfer through a licensed gun dealer, which will involve some paperwork and a fee.
Some people sell privately owned firearms through dealers even though it isn't required in that person's state so there will be a record of the sale.
Also, regarding handguns specifically, in the U.S. you can only purchase a handgun within your state of residence, so if you are selling a handgun to someone in another state or if you are purchasing a handgun in a different state that where you reside, that must go through a licensed dealer in the state where the purchaser resides.
Additionally, all of this applies to non NFA firearms. NFA firearms are machine guns, supressors (silencers), short barrel rifles and shotguns, and a few other things.
YES
Yes.
i think its privately owned
No, it is generally illegal to sell a gun to someone in another state without going through a licensed firearms dealer to facilitate the transfer.
at an illegal firearms store? No one here is going to tell you how to acquire an illegal firearm. It is illegal to purchase a stolen firearm or for a felon to purchase a firearm.
No
A private citizen of Oklahoma can sell a firearm to another resident of Oklahoma. They may also sell to a dealer or collector in any state if they hold a Federal Firearms License. The sale cannot be to a person you believe is unable to own a gun.
There isn't one, it's a privately held company.
You can list it on eBay or sell it privately to a collector.
No.
No
No, not illegal at all. Depending on the rules of the site providing the service many sell at local community internet sites along with cars, furniture, homes, etc.... Craigslist has a ban on it although they are legal to sell in my state, you can solicit sex on Craigslist which is illegal in my state but they allow it along with nude pictures. I dont like Craigslist because of this. Hope this helps