It can certainly look like powder but good product tends not to, and be in crystal form - even if microcrystalline form - instead. This is a tendency: a probability thing... but you cannot determine anything by it for sure. I guess that in some parts of the world it is common for the available K to be cut, even if a little bit, so going on the hunt for crystals could be pointless and/or fruitless.
There is no way to tell them apart, I have tested offered K on the spot (well not in public) to see what kind of potency it was. I have gotten potent powder that I was underestimating.
We indeed don't cover testing nor do we allow ID threads, so this will be the end of the matter. Good luck finding good stuff.