What the deposit is for
The drawing. Between the consult and the session your artist spends anywhere from two hours to two days designing a piece for one specific body, and that work happens whether or not you turn up. The deposit pays for a fraction of it and comes off the final session, so it is the first two hundred dollars of the tattoo rather than a fee on top.
It does not transfer. Not to a friend, not to another artist here, and not to a different piece a year later. It bought one person’s time drawing one thing for one body, and that has been spent by the time anybody asks.
Why one rate
The obvious commercial move is to charge more for the artist with the longest waitlist, and plenty of studios do. It is defensible and it is not what happens here.
The reason is that a queue is a measure of demand rather than of quality, and pricing by queue length means the studio has a financial interest in one artist being harder to book than the others. That is a bad incentive to introduce into a room with three people in it.
The estimate
You get an hour range in writing at the consult. If the piece runs over, it finishes at the estimate. If it runs under, you pay for the hours it took.
The asymmetry is deliberate: the person who estimated is the person who is wrong, and the client should not carry the cost of that. It has been the policy since 2014 and it makes the estimates conservative, which is the point.