Suppose there is a pack of mixed spices that does not have a reliable hechsher, but looks like it would be good for besamim. Would it be OK to use them for havdalah since you have no intention of eating them?
You cannot say a bracha on three kinds of spices: spices that are made to remove a bad smell, spices on an erva (someone you are forbidden to marry), and spices of non-jews. (See Shulchan Aruch OC 217)
Additionally it would be forbidden to smell objects which are assur behanaah (deriving pleasure from them is forbidden) because of their issur. These things include among other things meat&milk, orla, and yayin nesach. Presumably one would not make a bracha on something one is forbidden to smell.