I know I am not a parent, so I am probably the last person ever who should give parenting advice, so lets call this listening advice. When you are thinking about getting your child's haircut...
I do believe this problem could be solved by listening. If your child is showing the signs of being tired or ill, it is probably NOT the best time to bring them in for a haircut. This usually leads to crying and a fit once they get into my chair. This just causes trauma, which leads to fits and crying in subsequent haircuts. When you force your child to constantly get their hair cut in a way they don't like, then they are never going to want to get a haircut. Talk over options with your child, ask them what they would like their hair to look like. If your child wants it short, but you want it long, they will take matters into their own hand. You will wind up with this on your hands:
The best scenario is when the stylist and the parent can work together and figure out what works best for your kid. The only way for this to happen is consistency. Take your child to the same place, even to the same stylist. This all creates a safe environment for your child, and helps whoever cuts their hair to adapt their style to your child.
Last, and certainly NOT least, I plea, I beg, please change your child's smelly diaper before your put them in my chair. I don't have kids yet, and have not adapted to the smell of poopy diaper. It makes me puke! And if your child is of BO age, please smell them before your bring them in. I am not a robot... I have a nose too!