The store's two employees escaped unharmed and the fire was contained within 15 minutes, said Boonsboro Fire Co. Capt. Ed Gotthardt.
White smoke billowed from the shop's four front windows, which were broken out, revealing the charred interior of the building. A large orange sign remained intact by the store's front door.
The owner, Jimmie O'Neal, who had driven from his Cumberland, Md., store when he learned about the fire, paced in front of the lightly smoking building, shaking his head.
"I really have nothing to say about it," he said. "This is my living."
Moore, who had worked at the store for about a year, said he had just gotten off the phone with a customer when he heard his co-worker, Steve Strite, 22, yell from the workshop.
"I grabbed the water hose and he grabbed the fire extinguisher, but it was too late," Moore said.
"The smoke and fire just started taking over," he said.
Craig Davis, 28, assistant manager of the AC&T, which is next door to the lawnmower shop, said a customer had come back into the store to tell him about the fire. Davis called 911.
He said he was a little worried the fire would spread to the gas station.
"But the fire department responded quickly and pretty much blocked it off," he said.
About 50 firefighters from Boonsboro, Sharpsburg, Middletown and the Washington County Emergency Services Unit, responded to the scene.
Strite, 22, said he saw flames rising by his feet and yelled to Moore for help.
"I wasn't really scared," he said. "I seen the flames and tried to hit it and it didn't work so I got as much away from the building as I could."
Moore and Strite managed to salvage a forklift that had a lawnmower deck attached to it from outside the garage door of the building. The deck was charred from the fire.
Moore said most of the customer equipment was stored behind the building and was safe. A few lawnmowers were in the front parking lot, unharmed.
Strite, a mechanic at the store, stood expressionless while he watched the firefighters bustle in and out of the building.
He said, "I'm just worried about where I'm going to work now."