I made knives as a hobby. I have taken commissions but will not do so willingly again. I have read many discussion threads on US knife forums where makers far better and more experienced than I have said the same thing, and like me, they said that the decision to cease taking custom orders was a very good one.
There are a number of reasons for this. Some to do with the engineering/build process, some to do with the business side, and some to do with human nature and interactions.
Any time you are making a one-off commission there is more pressure and stress than when you are making your standard designs. It is easier to tell everyone "no custom orders" than to attempt to listen to ever punter describe what they want, discuss with them all the details and decide whether their particular request fits with your skills, tools and materials to minimise your stress and impact on other work.
One of the common remarks is that people wanting custom work often don't really know what they want, or have crazy ideas and expectations. Those that provide vague and open ended briefs are not much easier than those that send detailed specifications. They can still be disappointed when your interpretation of their brief doesn't look how they imagined or dissatisfied when their design for the ultimate fish filleting, twig whittling camp chopper doesn't work as hoped.
I have met very few knife makers who I would call self-satisfied with what they produce. All the best ones are super self critical. This is what drives them. They are also usually really poor at putting a price on their time. They know what the market at large asks for similar designs and are not comfortable asking much more. Some do, but they are in the minority. They are however acutely aware of the hours required to achieve a design and it tends to be a sore point if it takes a lot of time while they don't feel they can decently ask a lot of money for it. It makes it easier just to say "no" from the outset.
If someone wants a steel or handle material that you don't usually use it has to be sourced, if you mess up, you have to source more, and if you have any left over, you have to decide whether to use it up or keep it on the shelf. Materials left on the shelf don't make money, they just take up space. If it is a steel you don't usually use, how are you going to heat treat it? If you heat treat in-house you won't have a recipe for a new steel, so maybe you have to send it out. Sending out is expensive for just one or two blades and if you haven't used the steel before there is a decision over where to send it and what to ask for. Is the construction in line with what you usually make, or are you being asked to do something that you have not yet figured out?