I could stomach a reasonable limit on the number of samples tried. Something like 8-12 would be reasonable IMHO, and only after the customer has described what kind of flavor is being sought. i.e., tobacco, fruit, candy, coffee, baked goods, etc. You should be able to holler "that's it!" after trying well nigh a dozen.
Pay per puff sampling is just plain stupid. Either the policy won't last, or the business won't.