Sometimes, bulk stores have multiple suppliers. Some wash well, some don't.
More likely, they always wash well at that store, but sometimes some slip through. Also, if sometimes you're taking from "the bottom of the barrel", the last seeds in a particular batch, they'll be much more potent than those at the top, due to settling. Atbulk stores, always dig a bit and take seeds from near the bottom.
Most likely, they bought a lot of seeds once, from different suppliers. Prices change, you know? Sometimes they'd buy from one supplier, cause they were cheap at the time, and when the price increased they went to another cheap supplier. Unfortunately, one of them washes well, the other doesn't. Then they either just mixed the two types together, or alternate them out in the bulk bins, one week one supplier's the other when it runs out, and so forth.
Your only option is to try to find a different bulk store. I really think they must have some seeds that are washed, unfortunately, and they're either mixing them in or alternating to them, and there's no way for you to tell, really. I suppose you could bring a small bottle, buy 100 grams of seeds, then make a mini-tea with like 80-120ml of water. After filtering, if it tastes SUPER bitter, then you know it's safe to buy, get a bunch NOW. If it isn't bitter, the crap-product is out, don't buy, come back and try again later. Make sense?
I use bitterness as a fairly accurate potency guage with seeds. Anyway, good luck, man.
