Well I am glad to hear he seem to be pooping solid poos again. That is great.
It is not the store itself that is at fault but the supplier. Being such a massive breeder there will always be a proportion of animals who will become ill. I am sure that the animals are raised in good conditions actually as it would not be in their own interests to have ill animals. The main problem is caused by the lack of human contact which means that the babies are under a great deal of stress when they leave the supplier, then more stress in a big shop display and then again in a home move. Weaker animals will succomb to disease and as they are not particularly selective about breeding for health as a hobby breeder would be, looking more for attractive colours and patterns which appeal to the public than the most healthy robust individuals.
That is not to say that they are not lovely hamsters and lovely pets. With time and understanding they soon tame beautifully and make wonderful furry friends. They just do not get the best start in life. Most stores have caring and knowledgeable staff and if you are in any doubt you should ask to speak to the head of that department or the manager. You should also report any problems to their Customer services dept by e mail.
We do prefer Harry hamster food personally as it does contain a Prebiotic which feeds the bowel bacteria and maintains a healthy bowel. We have never had a case of wet tail when using Harry (fingers crossed) Most of our friends also use this food. If you wanted to change you need to make it very gradual and if he does not eat as well on it then probably best to stick to what he does eat rather than risk problems. I would keep a record of his weight and make sure he gradually grows.
Good to hear he is nice and tame already. This indicates he is less stressed. Is he still on the Baytril?
The coconot house may get a little small for him soon so watch the size of it. They are also a bit hard to clean if they wee in bed
So what do you call him? He sounds like a long hair if he is fluffy and maybe a Golden?