"Are you a sales person?"

Translation: Ви продавець?

[tyndermynder]

you can also ask a friend if he is a salesman so I think it shouldn't be formal only

[SmithUA01]

agreed. the justification for "it HAS to be vi" is artificially narrow

[KirstenBenites]

Agreed, ти should also be accepted.

[GeninMage]

Just got "Normally, you would use polite form here, since likely you are talking to a person which you don't know personally. So it has to be 'Ви' here." Someone commented that you can ask a friend this question as well 3 months ago...