The client arriving with somebody else's mistake

A correction is not a service with a price

The same request can be one appointment or four, depending on what is on the hair, how much of it, how it was processed and what condition the hair is in underneath. Any figure given before someone has seen it in person is not an estimate, it is a number the client will hold you to. The honest structure is publishable though: a consultation first, a price after it, and a plan that may run across sittings. Saying that clearly is what separates a salon that takes corrections from one that dreads them.

Never comment on the other salon's work

Not in agreement, not in sympathy, and above all not in generated text. "That shouldn't have happened" is a judgement on a colourist nobody has met, about work nobody has seen, put in writing by software. It is also the sentence a frustrated client is inviting, which is why the refusal has to be configured rather than left to tone. Sympathise with the person and say nothing about the work.

The photograph helps and does not decide

Ask for one - it is genuinely useful, and it tells a colourist more than a paragraph can. Then say what it cannot do: screens lie about colour, a photograph cannot show porosity, previous chemistry or how the hair behaves wet. A salon that explains why it still needs to see the hair sounds professional; one that quotes from a photograph sounds confident and then has to renegotiate in the chair.

Say what happens if it cannot be fixed in one visit

Sometimes the answer is that the hair needs weeks before anything else is done to it, and that is the hardest message to deliver and the most valuable. Publish the possibility in advance - that a correction may be staged, that the first appointment might be an assessment and a treatment rather than a transformation - so the client hears it from your page before they hear it in the chair with their coat still on.