The customers, who are also a father and son, had visited the store to collect a firearm that had been dropped off for repair. They became irate after being told it was not ready and there would be a $25 service charge, the Pearl River County Sheriff's Office told WDSU.
The argument descended into a shootout, resulting in the owner and his son dying from "multiple gunshot wounds" and the customers being transferred to intensive care, Sun Herald newspaper reported.
The case is still being investigated and no charges have been filed, the newspaper reported Sunday. NBC News was not able to reach the Pearl River County Sheriff's Office for an update early Monday.