Huh. I could've sworn when I first read this post that the pet store was listed...
If it was a PetSmart store:
I think I might have mentioned this before, but it's been a long while since I've posted. If you see anything wrong at a PetSmart store, please report it. We do care about the animals at the stores. Ignorance needs to be corrected. If the employee won't listen to you, take it to a manager. If the manager won't listen, then corporate most certainly will. Try posting what happened on the PetSmart facebook page and see the reaction you get.
The methyl blue is to prevent several diseases (velvet, fin and tail rot, ick). PetSmart is phasing it out of use at the stores, though the warehouses will still be using it during shipping. If you go into a store and some of the water is blue and some clear, the ones in blue are the new fish, the ones in clear have been at the store for at least one water change. If there are no bettas in clear water, then that store has yet to phase out the methyl blue.
The temperature of the tank water is usually 76-78 degrees. The store's room temperature will vary depending on whether colder temps have hit your area or not. Summer/warm weather maintenance temps are 78, winter/cold weather maintenance temps are around 70.
As for icky things in the water, the nitrite and ammonia levels of the store's tanks should be at 0. The nitrates can be as high as 40 before action is taken, but, considering that the fish systems at the stores do automatic water changes, it's rare for them to get above 5. It's pathogens, more than chemistry, that you'll need to worry about. We use UV sterilizers on the system water to prevent the spread of diseases, but that doesn't stop individual tanks from having something wrong.