I dont think it is the job of a supply house worker to police what people are buying or what they do with it once they purchase it.......
It is one thing to provide technical assistance including advice aimed at discouraging a customer from purchasing a certain circuit breaker, but the actual purchase should be left up to the customer.
If the customer's home or a client of such a customer's home was to burn from an improperly installed circuit breaker, the law will take into account the person's knowledge, experience and perceptions when the time comes to determine if the "contractor" has acted reasonably. Conduct is judged by considering actual knowledge of a person.
Reasonable, ordinary people know icy roads are slippery, downed overhead conductors are dangerous, alcohol impairs driving abilities, children may run into the streets while playing, but a person who undertakes an activity such as installing a circuit breaker is ordinarily considered to have the special skills and common knowledge to do so.
If special skills, education and training are involved, the bar gets raised a little. Often licensing is involved. Anyone who performs these special skills, whether qualified or not qualified, will be held to the standards of conduct of those that are considered professional. The "trunkslammer" is held to the same standard of conduct of persons who are reasonably experienced.
I would rather have my rights in place and be able to purchase anything that is for sale in an electrical supply house than to be singled out and judged "incompetent" by a sales clerk concerned of my apparent lack of understanding of wiring methods.