you can also ask a friend if he is a salesman so I think it shouldn't be formal only
agreed. the justification for "it HAS to be vi" is artificially narrow
Agreed, ти should also be accepted.
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...