I remember Spacevets!
I am not sure why the puppets would be made in huge numbers, Dogsbody wasn't as famous as most other BBC puppets, so is less likely to be involved in a scam as it isn't like hundreds of people would want one, or fakes would be made? Are you able to see it before you buy? If it is genuine, and you have the pictures of it, and can authenticate it, I would personally go for it as you are not likely to have the opportunity to buy a childhood 'friend' like that again. But you must prioritise what is most important to you at the time.
I just know I'd love to have a real 'Gordon the Gopher' one day, but it isn't likely to happen!