I do it full time, but for me it was all part of a plan. To explain, I retired from the military about 8 years ago. I've been making knives since about my 4 year point in my military career. After attending my first couple of knife shows, it was very evident to me that in order to do this full time, and still enjoy it without it being unduly stressful, would require something more in the way of income. One of the primary reasons that I "stuck it out" and completed a military career, was because I knew I would have a steady retirement check coming in, and also very affordable health insurance for the rest of my life.
I can remember in my early days of knifemaking, thinking just how "rich" all the "high profile" makers must be, and hoping that maybe someday I might get there too. What I discovered as I "climbed the ladder' was/is that even the majority of "high profile" knifemakers who do not have other sources of income, live a VERY meager existence, in many cases hand to mouth. I only realized this a few years ago, while talking with a group of makers at the Blade Show. Listening, I found myself astounded that many of them spoke of how they had to sell the knives they had brought to the show, in order to get back home! One even mentioned that he had taken out a loan so he could attend the show.
In reality, the facts are that nobody "needs" a custom knife. Any money that a custom knifemaker makes is based on somebody else's disposable income. If times are such that people either do not have disposable income, or perceive they do not, then custom knife sales decline.
The key to being successful as a full time maker is diversification, just as Dave mentioned. I not only produce custom knifes, but also grinder platens, custom grinding and heat treating, forging hammers, forge plans, as well as offering Knifemaking classes, and teaching at various events around the world.
There is a saying among many full time knifemakers....."Behind ever successful full time Maker, is a spouse with a really good job!"
All of this basically applies to just about any "craft" where "non-necessity" items are concerned.