Not a knife maker, but a business owner and these are some of the top: Customers who assume they are more knowledgeable than you, if that's the case, do it yourself. Customers with vague initial requests at the beginning that turn into particular complaints at the end, we cannot read minds. Customers who do not accept our timeframe or have an unrealistic idea of it, telling us you need X done at Y time is okay if done beforehand as we can tell you if it's possible, telling us halfway through will just leave everyone angry (note: if we don't deliver on our estimated timeframe that's on us). Customers only focused on price, or who are trying to leverage competitors pricing against us (note:I don't blame them, everyone wants dollars to go far, still annoying) we are not our competitors, we are not the cheapest in town and there is a reason. Customers that are simply rude or thankless, we pride ourselves on being pleasant and professional, don't ass it up on your end.