They arrived in the city just before 11 p.m.
Davis, who was driving, said she was nervous as Cook got out of the car to meet the seller.
"I told Danny I had a bad feeling," she recalled Tuesday. "It seemed too good to be true."
Cook left the money with her and went to meet the seller. They walked around the corner and into the darkness.
Then shots were fired.
Terrified, Davis said, she raced toward Cook, who had been shot in the back and a leg. One of his shoes lay in an alley.
It appeared that Cook had tried to run from the gunman, Davis said. His pants pockets were turned inside out, as if the shooter had searched them for the $950.
"I had that money. There's no way Danny would have told them I had that money," Davis said. "Danny lost his life protecting everyone else's life."
On Saturday, Thomas Coffee, 23, of Willow Grove, was charged with murder and weapons offenses in Cook's death.
Davis and Cook's family are left to mourn.
Davis and Cook, both 27, had been a couple for two years. She called him a devoted father of two children, 8 and 5. He was a passionate biker who had been looking forward to a new ATV.
"All Danny wanted in his life was to race and have four-wheelers and have dirt bikes and ride with his friends in the woods," Davis said.
"It's so wrong. He does not deserve this in any way, shape, or form."
Cook was a self-employed landscaper who worked side jobs as a mechanic. He and Davis lived in Williamstown, and he was also helping her raise her daughters, Kelsey, 8, and Kylee, 4.
"All he cared about was that my children had everything they needed every day," Davis said. "I have to keep it together and keep my composure together for my children, because if they see me crying, they are crying. . . . It's hard."
Relatives, too, are grieving.
Outside Cook's family home on Tuesday, his cousin Jennifer-Lynn Quinones read a statement saying Cook "enjoyed life and lived fearlessly through the journey."
"He was a son, a grandson, a cousin, a nephew," she said as an uncle who had flown in from Minnesota to attend Cook's funeral stood nearby.
Quinones said her cousin could tell what was wrong with a car by listening to the engine's roar, she said.
As a child, Cook tried to outfit his BMX bikes. Then he turned to toasters, she said, trying to fix them with screwdrivers.
"He was always a fixer," she said.
Tony Vega, the uncle from Minnesota, called Cook "a motor head."
"He loved to race cars. He loved to work on cars. Anything that had to do with cars, he was all over it," Quinones said. "The kid could do amazing things with his hands.
"His passion was cars, family, and the love of his life," Quinones said.
She recalled that her cousin had told her how much he loved his fiancee.
"I never thought about making anybody my wife, and then I met her," she quoted him as saying.
Asked about the killing, Quinones said: "He wasn't doing anything wrong. He was just answering a Craigslist ad."
Funeral services are scheduled for Saturday at Helping Wings Pentecostal Temple, 520 E. Stanger Ave., Glassboro. Viewing hours are 1 to 3 p.m.
Contact Sulaiman Abdur-Rahman at firstname.lastname@example.org, or follow on Twitter @sabdurr.