The one that is actually about the room
Rule two, and it is the only thing asked of anybody here.
Two chairs two metres apart means the room is shared. Somebody having a work call at one chair is a work call the person at the other chair is also having, for its entire duration, while unable to leave. That is the whole reason, and it has nothing to do with etiquette.
No one here will comment on it. But it is the rule we would keep if we had to lose the other five.
On gratuity
The card reader here does not ask. That is a deliberate setting and it costs real money.
A prompt on a screen while somebody who has just spent two hours on your hands watches you choose a percentage is not a request, it is pressure, and it is applied at the least comfortable possible moment. Prices here are set so the work is paid for at the price. Anything on top is genuinely a gift.
No product wall
There is one thing for sale in this studio: cuticle oil, at cost, and it goes home free with every removal anyway. There is no polish line, no hand cream, no branded anything.
The reason is small and real: a studio with a retail wall is a studio where the artist has a second reason to mention a product, and you spend the last five minutes of your appointment wondering which reason it was.