Jack Vance’s writing is of such quality that one wonders if one should really believe his numerous affirmations indicating that he only worked for money.
Here are ten statements taken from various interviews that shed light on the subject (without however ending the debate!)

(Broadcast – hour 25 – 1976) :
VANCE: Leaving the field? I can’t afford to.
When I make as much money as Silverberg does, then I’ll start thinking along those lines

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VANCE: But actually it works out, as far as my own career (so to speak) goes that the better I feel I’ve gotten to be as a writer, the more money I’m making. I’ll probably never be wealthy, but over the last few years I’ve become a lower middle class type. Probably don’t make as much as you fellows do… (Laughter)
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VANCE: Actually, there’s very few science fiction writers that have made any money at it.
Heinlein…, Asimov has made quite a bit of money, but I don’t think he’s made so much from his fiction as he has from assorted other stuff.
Silverberg has made a great deal of money, and he tells me that he’s made most of his money out sf his non-fiction rather than his fiction.
Frank Herbert has made a great deal of money.
He’s made it primarily out of his… First of all, he made a reputation with a book called – it was originally UNDER PRESSURE – then it was called THE DRAGON IN THE SEA or something like that. This established his reputation, and then be produced DUNE, which of course approached ‘best seller status – not just science fiction, but became a well- known book across every phase of society. Well, Herbert’s made a lot of money.
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VANCE: You just can’t help it. Now I’ve often wondered if… I don’t know what his name is, but if he approached me and said, « Vance, come write some Star Trek things… »
HODEL: His name is Gene Roddenberry.
VANCE: I’ve often wondered what I would say, you know. I’d say, « Well, first of all, how much? » And then I’d say… Well, essentially I’m not going to do it. I could be tempted with more money than he’s got in his budge…, but essentially I’m just not at all interested. And he’s not interested in me as far as that goes.
../..
What made you start writing science fiction?
VANCE: Well… oh, I don’t know. Hard to say. I really can’t put my finger on it exactly.
HODEL: Probably wasn’t the money. When you started in the fifties…
VANCE: Oh no, I wasn’t making any money at all, because I wrote lots of stories which never got published.

SF Review 1977 :
VANCE : I wanted to see if I could make any money in suspense, murder so I started writing these things. I stopped because I make more money with science fiction and fantasy.

Aberration mag 1996
« Long, long ago, when I was trying to find a voice, as we used to say, I thought to myself, ‘the only way I’m going to make any money—at a half cent a word—is to become a million-word-a-year man.’
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« But I didn’t mind. I was scared to get attached to that big money; that if I got dependent on it, I’d suffer if I ever got kicked out But I got kicked out before I could get acclimated to any big salaries
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« Not enough money in mysteries I’d like to do mysteries if someone would pay me for it. If I could make as much money doing mysteries as I do the junk I now turn out (junk’ is an affectionate term).

Utopia France 1998
I ask him if he doesn’t want to write new mystery novels in the style of Bad Ronald or Lily Street. He says no.
– Too much work for not enough money!

Slash mag France 1998 :
…Ellery Queen gave me $3,000 a book. That was money then! In the contract I was required never to reveal that it was me who wrote them. Theoretically so I never took the name. Anyway, he took my good prose and stuffed it to death to make his own little soup.

Broadvast WDR Germany 1999
I couldn’t sell enough, back when I got married, so I became a carpenter and built houses – for a few years until the money I earned from the stories was enough.

Faery mag France 2001 :
Do you think your worlds would fit well on the screen – in the form of movies, video games?
Vance : Well, in these situations, you trade your artistic control for money, but sometimes it’s the cost of survival.

Sf Weekly 2002 :
Vance…I was a carpenter for a time and everybody watches what you do. In fact, almost every job you get somebody watching you.
Even the job you have now as a writer.
Vance: I don’t care about that. I may have worried about that when I was very young, but when I started selling stories I didn’t think about it at all. I just wrote what I felt like writing since they seemed to sell. I never made lots of money at it, but I sold enough. I never wrote for the public. Never. If I had, I would have been writing Star Treks.
What was the writing and publishing climate like when you started writing?
Vance: Very hard to crack. Hard to get into and you couldn’t make any money at it. I worked for half a cent a word. I’m not a fast writer to begin with, so for the first few years I had do other things. As I mentioned, I was a carpenter for a time. Then I worked for a company that put in building partitions in offices. A pretty good job. I had a van to myself and I could run around more or less on my own time and slap together these partitions.

JVMB questions 2003 :
Why was The Genesee Slough Murders never realized?)
Jack’s answer:
Bob Ockene, the editor for the first two Joe Bain books, died of leukemia. When I wrote the outline for Genesee Slough, I never did flesh it totally out; I never got the story really plotted to my satisfaction.. but for one reason or another, the new editor at Bobbs Merrill turned it back, I don’t know on what basis. But I kind of gave up writing that stuff, the stories werent making any money for me, particularly .. of course nothing was making any particular money for us, in those days (1966)

Locus mag 2012
‘‘I wrote to make money, not for any other purpose. I just wrote the stuff because I was pretty good at it, and I wrote as fast as I could. I don’t glorify my writing at all. For some reason I have the knack. I can’t take any credit for it, any more than you can take credit for being a beautiful girl.