If I buy plants from a non-native plant source, I always ask if their plants have any on them. If there is the least bit of hesitancy in the part of the employee, or the higher ups they ask, I don't buy it.
What saddens me terribly is my local, family-owned general purpose nursery uses neonics. I preordered some butterfly weed from him in the winter, saying No chemicals of any kind. He did this for me and I think I ended up with five flats of butterfly weed, but I want to support the owner. He had one good sized butterfly weed that I would have purchased, too, but asking about neonics, yes, he put some on that one. I grieve for the person who bought that thinking they were helping Monarchs.
When I asked him about this, especially since people want these plants for pollinators, why he does this? He said people want perfect plants and they will not pay for less than that. I am hoping more people are bringing this up to their local nurseries so their practices can change for the better.