How to tell if 'beeswax' bars are real beeswax?

I've seen beeswax from wild bees that made their hive inside a burnt-out hollow tree - the wax would be smoky. The hardness could simply be due to age. Beeswax will get harder the longer it sits. If the beeswax was wild-harvested from an old hive, there's no telling how old the wax actually is. If you are concerned, you could melt it slowly and gently in the top of a double-boiler. Once it is well and truly melted, you should be able to skim off anything that rises to the surface and then pour off the liquid into molds, leaving behind the layer of gunk that sank to the bottom.