The gun store owner did a very brave and courageous thing to warn authorities, and the FBI really should do a better job of keeping an eye on folks that are reported by these "boots on the ground" citizens. These people have their pulse on the streets and their intuition should certainly be leveraged.
Every time something like the shooting in Orlando happens, we find out that there was somebody who saw the warning signs that something bad would happen and the authorities do nothing. I am not saying they could have prevented that but they could have used their resources to follow this suspicious individual. Instead of worrying about ordinary folks they should have been worried about that guy.
The FBI was warned by a gun store owner about the Orlando shooter. The agency should have paid more attention to this report. Especially since the Orlando shooter had previously been on the Terrorist Watch List. He should not have been allowed to buy any firearms, and the FBI should have detained him for questioning. In short, the FBI needs to pay more attention to warnings from gun store owners.
This is a very shaky topic because from one side you do not want the FBI wasting their time on false leads, but on the other hand you cannot be too careful when it comes to gun safety. Considering the fact that the FBI are seen visiting people for suspected bomb threats over the internet, it is safe to assume they have enough resources to respond to these reports.