Pinch a small lump of hash (about the size of a matchhead) on to a flat enamel surface or ashtray, and play the flame of a lighter over the hashish for a few seconds.

If it's GREAT hash it will light on the first or second attempt. The harder the piece of hash is to light, the more likely it is that you've been sold a 'lemon'.

Once you've got your test piece of cannabis in flames, let it burn for a couple of seconds and blow it out...