Brian Tolmie was initially amused when William Cochrane offered a bike and a dog in exchange for the car his friend was selling.
But their hilarity turned to anger when they realised the dog had been stolen from a young family in Inverness.
Along with Ms Straube’s ex-partner, Mr Tolmie posed as a potential buyer and the pair met William Cochrane..
But instead of the deal being completed, Cochrane was arrested.
Mr Tolmie, a 25-year-old labourer from Fort William, also has a dog, a two-year-old cavalier King Charles spaniel, and knew what Roxi’s owner would be going through.
He said: “We had a good laugh at the spelling when Cochrane sent an e-mail, and even more when we saw what he was offering for the car.
“Around half an hour later I was on the website, Missing Dogs Scotland, and noticed Roxi and thought right away that it was the same dog.
“I contacted Anna and, just to make sure, I asked her to send a more detailed picture by e-mail, and when I received that, there was no doubt that it was the same dog.
“This was on the Sunday, and by the Tuesday we had arranged to meet up with Cochrane and carry out the deal – I came straight from work at 5pm and we arrived in Inverness around 7.30pm.
“By this time we had masses of e-mails and texts, and enough evidence for the police, but we wanted to make sure 100% that we had the right dog.
“When it recognised Anna’s partner we knew right away and we called the police.
“As a dog owner, I put myself in their position and that was the reason I decided that I would try and get Roxi back to its rightful owner.”