welcome italian fellow!
I also bought a piggie at the shop many years ago, you know here in Italy we have very few rescues (and also very few piggies on sale). I was lucky and you also had luck with yours. But where do pets on sale come from? there was a report tv programme some weeks ago (by Le Iene) and it explained how illegally puppies and other pets are breeded before going on sale into shops. Maybe abroad the situation is different, maybe there are serious controls, but in Rome last March there was a great requisition of a huge herd of guinea pigs aimed at the shops' customers. Most of them seemed to be healthy and had been treated with medicines. But I wonder: what kind of medicines? what kind of antibiotics? maybe also the healthy ones had a damaged gut for the use of inappropriate treatments... You know, there are no serious controls in breeders producing the meat we eat, who knows what happens with pets' business...
For this reason I say, it is better to go to a serious breeder or to take a piggie from a private who had a not wanted pregnancy at home...