I'm sorry. Nido has hit a lot of collections hard and it seems like in the past year we're hearing more and more about it.
The seller may not have even known it was sick since was eating and appeared outwardly healthy. Often the stress of shipping can cause it to flare up if the snake is carrying it.
If you search for "nidovirus" on Youtube you can find videos with experiences that other breeders have had. Some lost a lot of animals.