Rats in a pet shop

Question
I am filling in at a pet shop I used to work at. Its tiny with only one person working at any given time. Someone brought in their three rats in a wire, 3 tiered cage which has wood based cat litter in the base, but it is not accessible by the rats.
One of the rats has been sneezing since he arrived, they are just over a year old. I was hoping it was just from the change in environment, but have noticed a little bit of mucus around the nose and now one of the other rats is starting to sneeze.
The owner of the pet shop is not a fan of rats so he leaves them for me to deal with. He won't pay for them to go to the vet. Do you have any advice on what I can do to help them? The shop is a little draughty cause I have to keep the door open and its getting cold now. I tried to cover them up but the owner got mad and removed the cover.
I am also worried that if he doesn't sell them in the next couple of days he's going to kill them and sell them as snake food. Could really do with some advice. Thanks!

Answer
Chloe-

Sorry for the delay.

Many rats will experience sniffles and sneezes when they first come into a new environment. Mucus from the nose could indicate an respiratory infection or it could just minor irritation from all the new smells. Respiratory infections can be treated with Baytril. You can purchase it from pigeon suppliers- you might even carry it in your pet store.

I do hope that these little guys have found a new home since your letter.