I've heard guys take brick weed and spray it with Raid ant killer and sell it as dank because of the head trip. It's unlikely that you'll come across something like that. You can usually tell by the appearance, smell and taste. If it looks like the crystals are just grains of sugar that have been sprinkled on or if the bud is just one dull green color or if the smell isn't natural, but it still makes you ripped, maybe it's laced. You can usually tell by bag appeal