Bill heard, for example, that a dog matching Bella's description was seen at a motel near the office. She was reportedly playing with a family near a white van.
By the time Bill arrived, there was no sign of Bella.
Another time, Bill got a tip that there was a dog in the bushes about half a mile from his office.
"I saw what looked like the back of a dog's body sticking out of the bushes," he says. "My heart sank. I was nervous as hell. I pulled it out - and it was a stuffed animal."
Last Tuesday - three years after Bella's disappearance - Gerstein got another tip. This time, it was from PetKey, the organization he had registered Bella's microchip ID with.
The subject line of the phone message: "Bella has been found."
She was at an animal shelter in New Jersey - about 1,100 miles away. She had been picked up as a stray.
"I was just completely taken aback," he says.
He asked for a picture and, moments later, declared, "That's my dog."