Tupp, in actuality, guns are pretty heavily regulated. Even online or at gun shows - if you're buying a gun, you must fill out a form. That information is then sent to BATFE (Bureau of alchohol, tobacco, firearms & explosives). They cross-reference the personal information with their list of people who have been reported to them, that for one reason or another are NOT allowed to buy weapons. For instance, former felons and anyone with any domestic violence actions/reports against them.
Problems still happen - and people slip through the cracks - because each state has different criteria for reporting people who shouldn't be allowed to buy... and often, those reports aren't made in a timely fashion. This happened in the Texas church shooting. It was the AIR FORCE, of all things, that didn't get this guy's information turned in... so when the form was checked, the agency that says yes/no about whether this person can buy a gun... it said YES.
It's the old data entry problem: garbage in/garbage out.
That's only one glitch. People can and do lie on that form. The gun shop owner has only the person's ID to "verify" who they are. In North Carolina, there is another step in the process. The sheriff must issue a "purchase permit". To get the permit, you will need a notarized affadavit stating you are a person of "sound mind and high moral character". It's kind of an anachonism... and again, it's possible to cheat this too. But the local sheriff really WOULD know if there had been trouble with that individual, if there were any 911 calls related to them.
Now, to conceal carry a handgun... the background check is a LOT more stringent. There is a section where you must provide information if you've been under mental health care - and where, with whom and for what. Any previous legal problems. And all the other categories that can disqualify a person from owning a gun, by law. The sheriff then actually investigates each application and the applicant will be fingerprinted - and those prints will doublechecked against the gun ownership database. This makes it harder to lie. There is typically a waiting period that allows for the investigation to take place, before the permit is issued. It can be a short time, but typically it's 90 days. Longer in some states, and some states set the bar so high, that you must essentially claim and PROVE, that you have an immediate need for self-protection. These permits usually have to be renewed every 5 years.
In NC, there is a short-cut temporary "permit" for victims of domestic violence who are still being threatened actively. So those people can protect themselves, prior to being severely injured or killed even. It happens. Frequently enough, that these cases are seldom headline news anymore.
It gets more complicated than that - but this is the simple primer on what our laws are like. Yes, criminals can still buy a gun on the "black market" - from other criminals. Guns are stolen and then sold. (Mostly to get money for drugs.) And sales between private individuals still happen... but nowadays, the serial number is recorded and unless people are acquainted and friends... driver's license number included on 2 copies of receipts so that the transaction is documented.
So contrary to the internet memes, it's not all that easy to buy a gun in the US. There is a distinct process, that is designed to prevent disqualified people from buying, sellers have to be licensed - online or not; private individuals can only sell a small number before they are required to be licensed; and yet, bad people with evil intent have a lot fewer hoops to jump through. They just need to know somebody who knows somebody who sells guns outside the system. No, they're not nice people either.