I took a poundie from somewhere in Lincolnshire. It was meant to be going down to a forever home on the South coast. This was through another forum, the dog was advertised as being at risk on that forum and a member said they'd have him. No rescue was involved.
On the morning of the run, I went North to do my bit of the run, picked up the dog (a wired haired parsons JRT kinda thing) and headed South to the next pick-up.
On the way back I got a call from a rescue person who I know and respect. The person offering the dog a home was known to her. She was a serial rehomer - acts on a gut reaction to help, then gets rid shortly when it doesn't fit in. A bit more rooting about confirmed my suspicions, so I called the girl who wanted the dog and whe was very 'whatever' about it.
Fortunately, at that point, I was running a greyhound rescue, so we took the shortest, hairiest greyhound into the rescue and, amazingly, rehomed him less than 2 weeks later.
It can go wrong. On this occasion I was lucky to have kennels I could put little Frisby into, but not everyone has that back-up.