If the only samples were decaf, the "get you over the 2pm caffeine slump" effect would be diminished. This is one of the reasons I recommended juice samples without nicotine.If a coffee roaster gave out free samples (enough to get you over the 2pm caffeine slump), I can see that easily getting abused by neighbors who don't want to drop $3 at starbucks.
(There are other good reasons for it as well: if the samples have a higher nicotine level than the customer vapes, the flavor can be masked by nicotine burn, rendering flavor sampling unhelpful to would-be customers.)