I've never heard about buying a spayed rat in Switzerland. Guinea pigs, yes, but not rats.
I'm all for rescue centers. But considering that the life-span of a rat is 1.5-2 years, which is nothing, if you adopt a rescue rat you may have only a few months with your animal...
That's why I eventually stopped adopting rats. I would get so attached to them, and they leave us so soon, it was a drama each time. .