Years ago I used Black Gold castings (back then they were referenced/labeled as 'castings', where as, after, I assume, being confronted with the % of impurities, over a decade ago they changed their label to say 'worm compost,' as it wasn't strictly castings, and I had noted that it appeared to be less richly black over time).
Where I am, in the more northern area of Interior Alaska, not withstanding trips to Anchorage (da' big city for us) a good ways to the south, the two primary, 'seemingly' of quality, brands of castings are 'wonder worm' (pretty proud of their stuff, and spendy) and 'wiggle worm' (already mentioned in this thread.
Shipping to Alaska, even for commercial outlets, whether using barge and container cars, or trucking, is a pricy thing for the final cost to the consumer, thus we often pay a fair bit more than many of the folks have referenced who live down in the lower-48. (i.e., I would LOVE to get fresh, clean, local castings for $10/bag).
We run a larger compost pit or two for our family's scraps, as well as refuse from the veggie garden, and I'm sure there's worms in there, as I find them (a bit surprisingly, for how far north we are) when we harvest spuds, in fairly decent numbers. But as a rule, I don't use any untreated compost from the bins any place other than in the veggies. The chance of importing disease worries me.
Soooo, any serious qualitative knowledge re. comparing 'wiggle worm' versus 'wonder worm'? (*The only place I can get wonder worm, my preferred castings, for something that doesn't make me pass out from sticker shock, is in Los Anchorage).