Myco us super contagious. Back in the day when I had my first rat we'd be all freaked out and going to the feed store for antibiotics at the first sneeze.
I think by now though it's assumed that most rats have been exposed to it and some are just more resistant to it than others.
That's why it's important to avoid anything that could trigger problems like the wrong kind of shavings.
Moving to a new place is already pretty stressful and like fish I guess it's a those times that an infection may flare up. Perhaps jsut let them settle in for a day or two before handling them much.
I would probably check out different places to get the next two and prefer it when they keep their rats in pine-free shavings.
It's worth it to me to pay a few bucks more for a pet if it has a better chance of being healthy.
I think Polly's has Dumbos and I know Petsmart has Dumbos too.