I knew someone who had a semi trained sniffer dog. It failed training, due to being too excitable. While it was rehomed via a rescue, I believe that was mostly to them already have the procedures to vet people etc. There is also a good chance they acquired the dog via the same shelters.

And yes, he did use it’s training to identify who he could buy/bum a joint off of. The dog would get VERY excited to help, while down the pub.