Shambles,
To be honest that vibes with my experiences, my first batch of JWH-018 was from a 100% legit supplier, if these guys say it's an 99.9% assay, it's 99.9%. This was an excellent high at very low doses, a fine, slightly off white powder with some small, consistantly sized, lumps.
Later foolishly went with a closer, and cheaper (but still well regarded) supplier and recieved 1g of a pure white power, I've not tested this batch that thoroughly, but my first impression was that it wasn't as good as the first I'd tested. It was still a marked, defined high, but felt somehow different with more paranoia in my opinion. I now believe this to be 073, I would like to test the theory and am looking into methods of testing.
Today I recieved another batch of JWH-018 from another, also trusted supplier and this resembles the first. I've yet to test but first impressions are good.
On an unrelated note, I am now testing an eyeballed 2mg dose of the brilliantly shiny 081, this has a similar but considerably weaker odour than the 018 and have been advised by the supplier that it was made in the same lab. It is made up of distinct flat, square crystals which I can only describe as looking exactly like glitter (no really, I smudged some on my hand and now it sparkles...)
Will post a report once I actually smoke this thing rather than typing this reply.
Sheep and Drizzle hey Shambles

Noswaith da to you sir!
[EDIT]
What the bloody hell happened to the replies above this post and below my previous? I certainly did not imagine them...
[EDIT]
In fact I did.