Pasco County deputies say Wayne Justice showed up at his New Port Richey store to conduct business as usual on Sunday with a frequent customer.
Until that customer pulled a knife and Justice shot him in the chest, killing him, according to Pasco deputies.
Jacob Sanborn, 25, called Justice to set up a meeting to sell a few items to Justice at his business, Justice Rare Coins and Collectibles, 10030 State Road 52, according to the Pasco County Sheriff's Office.
When Justice, 52, arrived at the store at 9:46 a.m., the meeting turned into robbery, deputies said.
"(Sanborn) was behind him and put the knife to (Justice's) head and the business owner became fearful for his life and at some point was able to get away and pull his weapon and shoot the suspect," Kevin Doll, Pasco County Sheriff's Office public information director said.
The shooting took place inside the store.
Pasco fire rescue arrived and found Sanborn outside the front door of the business, taking him to a local hospital for treatment. Sanborn later died from the single gunshot wound to the chest.
Justice, who suffered a cut to the head that needed stitches, has a permit to carry a concealed weapon, Doll said.
"At this point it looks like it's just a simple case of attempted robbery," Doll said, "and the store owner defending himself in the act."
According to Doll, the sheriff's office forwarded the case to the State Attorney's Office.