Suddenly, chatter and laughter filled his shop.
Sixty people had just stopped in and they were ready to buy.
"I was shocked at the number that came in," Rust said. "It boosted sales, but more importantly it drew attention to the downtown businesses."
Like a flash mob, in which a group of people suddenly assembles in a public place and performs a song or act, the cash mob brought a group of local shoppers together and surprised a downtown business.
"Over a thousand dollars was spent in the store in a 30-minute time frame," said Mary Reynolds, Le Mars Main Street manager, who had organized the Cash Mob.
Everyone who wanted to participate in the mob committed to buying at least $20 worth of merchandise from the store, which was chosen just moments ahead of time.
At noon Thursday, the shoppers assembled outside the Le Mars Area Chamber of Commerce where Mayor Dick Kirchoff drew the lucky business' name out of a hat.
Any downtown retail Chamber member business was eligible.
The group bubbled with anticipation as the mayor drew out the name and read it to the crowd, who cheered before heading down the street en masse toward Rust's Western Shed
Le Mars businessman Steve Jester said he decided to join the Cash Mob to help promote the community's downtown.
"And it sounds like fun," he said, walking toward Rust's Western Shed.
Inside Rust's store, members of the Cash Mob laughed and talked as they showed each other tiny pink cowgirl boots, western shirts, sunglasses, leather belts, puzzles and greeting cards they planned to buy.
"It's a neat way to create some excitement in town," said Brad Pick, of Le Mars. "Everybody's excited to be here."
Cash Mob shopper Teresa Westra, of Le Mars, showed off her purchase: a pair of what she called "hoop bling" earrings.
"I think it's very important to support local businesses," she said. "And I thought this might take me into a store I might not have gone in otherwise. Now I know I can get cool jewelry at Rust's Western shed."
Rust said before Thursday, he couldn't quite wrap his mind around the idea of a Cash Mob.
Reynolds had explained to him that it was similar to a flash mob.
"I still was thinking, I don't get it, but let's try it," Rust said.
On Thursday, Rust's wife Jeannie was among the Cash Mob crowd.
When their store's name was drawn, she called her husband to give him a heads up.
A few minutes later the group packed into the store and started shopping.
"It turned out to be a better deal than I thought," Rust said. "I appreciated that people took time over their lunch break to shop downtown."
All the downtown businesses feed off of each other, he said.
"If anyone else's name would have been drawn, it still would have been good," he said. "It's going to be good publicity. It reflects on us all."
Thursday's Cash Mob will be the first of several.
The second will focus on other small businesses outside of the downtown area.
The third will be picked from a selection of downtown restaurants, while the fourth will be restaurants outside of downtown, according to Reynolds.
At the beginning of each month the Chamber will announce the date for the mob through the media, Reynolds said.
All are invited to participate in each Cash Mob.
After Thursday's event, Wendy Longtin, of Le Mars, said participating in the Cash Mob was an opportunity to find out more about the community's merchants.
"This is such a great way to get to know a business you might not frequent," she said. "Who knew they had all this other Western wear and accessories?"
She held up a full Rust's Western Shed shopping bag.
"I just stocked up on greeting cards," she said with a grin.