I will get flamed for this but here goes.  

No ID no beer or tobacco it's not worth your job or losing the license of the business owner. If they have non Amish friends with ids that are of age then let them come and get it.

You do not want the state or even the feds to come in on that. If a big enough problem is deemed in that area you will have something way past local cops coming in. No area wants visits from the ATF because licensing agreements are getting broken. 

While I respect everyone's belief's regarding alcohol and tobacco consumption and if that isn't for one personally then do not imbibe. However people of legal age (regardless of their religious background) do have every right to try it as long as they don't drink and drive or give it to under age people.

If the young guys are getting that angry and become combatative then let them know they have a choice they can politely leave or you can call the police and get them trespassed.

Just because they are Amish doesn't mean they are perfect nor should they have to try to be and I don't really care what they are wearing,  plain clothes or blue jeans and a Corona t-shirt.  Their relationship between what they do and God is personal just like every other individual.  I think it shows honesty to walk in a store with plain clothes and pick up a 6 pack and a pack of cigarettes. They are not put on this planet to be an example for other people's romantic notions of the perfect religion.