The kid obviously is a criminal mastermind since he walks in, goes to the counter, and politely waits for the man he thinks is his "victim". After a moment, he reaches into his waistband and pulls out his gun.
He's so gangster he even holds it sideways because that's how you know he's an expert.
The store clerk Steve Ewart is a man who was raised around firearms his whole life. Steve says, "I recognized it as a cap gun. It's a 1960s replica firearm." Not a good start for our would be bad guy.
When the punk asked for all the money in the register, Steve simple replied, "It's not going to happen". The intrepid crook asked if Steve wanted to test him. How did Steve answer?
"It's still only a cap gun, I'll test you all day."