The hardest skill in aesthetic practice is not technical. It is declining work that is standing in front of you with money in its hand.
There are a few situations where the answer should be no, and being able to recognise them quickly is worth more than any injection technique.
The first is when the expectation cannot be met. Someone brings a photograph of a face with different bone structure to theirs and asks for that. You can improve what they have. You cannot give them someone else's skull. If you cannot describe, in plain language, a result they would be happy with, do not start. The conversation to have is about what is actually achievable, and if that is not of interest to them, the treatment will not be either.
The second is when the request is being driven by something other than the feature. Sometimes people arrive at a treatment room because of a breakup, a bereavement, a job loss, or a comment someone made. That does not automatically disqualify anyone, but it should slow you down. A good marker is whether they can tell you what specifically bothers them about the area. Someone who says my nasolabial folds have got deeper in the last two years is describing a feature. Someone who says I just look wrong is describing something else, and more filler is unlikely to fix it.
The third is body dysmorphic disorder, and it deserves naming directly. Repeated dissatisfaction with previous work, a focus that moves from feature to feature, extended time spent examining the area, a history of seeing several practitioners in a short space of time. None of these is diagnostic on its own. Taken together they are a reason to stop and, if appropriate, to suggest the patient speaks to their GP. Treating into this pattern rarely satisfies anyone and frequently ends badly.
The fourth is simpler and more common. They are not suitable today. Active infection, a cold sore near the site, recent dental work, a course of medication you are not sure about, or the patient is unwell. Rebooking costs you an appointment. Proceeding can cost considerably more.
The fifth is that it is outside your scope, and this one requires honesty with yourself. Early in a career there is enormous pressure to take the case because turning it away feels like admitting a limit. It is admitting a limit, and that is the correct thing to do. Referring on builds more of a reputation than a mediocre result does.
How you say it matters. Do not hide behind policy if the real reason is clinical. Tell them what you have observed, what concerns you, and what you would suggest instead. Most people take it well. Some do not, and a small number will go elsewhere and get it done anyway, which is a genuinely uncomfortable part of the job. You are responsible for your decisions, not for theirs.
Write it down either way, including the reason. A note recording that you declined a treatment is worth as much in your records as one recording that you did it.