The RSPCA removed a suffering puppy from the Stow on the Wold Horse Fair in October following concerns for its health.
The underweight male puppy, which has been named Marley, is now in the care of the RSPCA Cheltenham & East Gloucestershire branch.
RSPCA chief inspector Lee Hopgood said: "The RSPCA and the police always attend the Stow Fair, and it is with the co-operation of the police we are able to resolve any animal welfare issues which might occur. In this case we had an immediate concern for the welfare of the puppy. He was checked by a vet who confirmed he was in a suffering state.
"We advise people never to buy puppies from Stow Fair or similar events as they are often suffering from poor health and many are from poor welfare backgrounds. We advise people to do their homework before giving a home to a puppy and never to rehome one because they feel sorry for it," said Lee.
Marley's health is gradually improving in RSPCA care as his weight slowly increases. Once the affectionate and friendly pup is fully fit he will be found a new home by the charity.
RSPCA tips include:
Do your homework to match the right dog with your home, family and lifestyle and that you can afford the long-term costs.
Phone ahead before visiting any puppies and know the right questions to ask.
Don't buy a puppy straight away - go home and take time to consider your choice and visit it at least twice.
Always choose a puppy based on its likely health and temperament and not just its looks - a healthy puppy is much better than a pretty one.
Never be tempted to buy a puppy because you feel sorry for it - another will only be bred to replace it.