I don't intend criticism of anybody else; we all have different ways of looking at our hobby (or profession, as the case may be). But personally I've never gotten interested in selling models. One reason is that I work so slowly that we aren't in any imminent danger of running out of space. Another is that I don't like deadlines. (I've had enough of them in my day job over the past 40 years - and in school before that.)
I used to take in model restoration projects, when I was a starving museum curator, but I never enjoyed it much. Quite a few years ago I decided I wanted to build models for fun and for no other reason.
Another reason I don't want to be in the model building business, frankly, is the wild variation in the prices for which models get sold. Yeah, $800 sounds like a lot of money. But if you divide that number by the number of hours you spent on the model, you're getting far less than minimum wage.
On the other hand, there does exist a small classification of people who pay huge sums of money for models. Back when I'd just finished my 1/128-scale model of the Hancock, the gentleman who ran the ship model gallery at Mystic Seaport tried to get me interested in letting him sell it for me. He said he figured he could get at least $15,000 (that's 1983 dollars) for it. Once I got done picking myself off the floor, I asked him what his commission would be. Answer: 40%. I guessed the model had about 1500 hours in it. I couldn't become a professional modeler for that kind of money. After thinking about it for quite a while, I decided to turn him down. My thinking was that, though I was far from a wealthy man at the time (I'd just gotten my teaching job, for $20,000 1983 dollars per year), the time might well come in the future when I'd need that money more than I did then.
Since I've been married, and raising two stepkids, there have been several moments when my wife and I have said "maybe it's time to sell the Hancock." But it's never happened; the model still sits in our den. I confess I've become pretty attached to it (as I suspect some people in this Forum have figured out).
A few months back I talked with my wife about willing it to a certain museum. Her response - to my surprise - was "not unless you can set it up so the museum doesn't get it while I'm alive." That one knocked me out just as effectively as the offer from Mystic did.
At any rate, there are dealers who routinely sell models for tens of thousands of dollars. I always wonder whether the people who buy them really appreciate, or understand, them. Some do. The Kriegstein brothers, owners of the famous Kriegstein Collection, give their models the same tender loving care that the best museums do. Others who play the game (I know of at least one of Donald McNarry's patrons who falls in this category) buy them because they're pretty and they're expensive - and know absolutely nothing about the ships or ship modeling. (The guy I referred to in the previous sentence had trouble pronouncing the names of the ships.) I've got better things to do than be patronized by people like that.
To each his/her own. I don't suggest that there's anything wrong with selling models - especially if you've got a space problem (or if you're now so sick of looking at that model, with all the mistakes you made ten or fifteen years ago, that you just plain want to get rid of it). But the stuff I build - and am proud of - isn't going to leave the Tilley house while I'm around.