[Kimberly Dow]

Webster's Collegiate Dictionary

sell out
1. to get rid of completely by selling.

"My Opening at the ___ Gallery was a sell out."

Now there is a positive connotation!

2. to give up one's artistic aspirations or moral principals so as to achieve success, financial gain, etc.

If an artist takes a commission that is not in keeping with their personal aspirations, (perhaps because they need the money to keep going or to get some exposure) that does not mean they are 'giving up' their principals.
Giving up would be if they never painted their own vision.

Selling out = giving up.

So you have two artists, one who paints full time and occasionally takes jobs that he is not happy about, but hey, life costs money. Most of the time he is very proud of the work accomplished. Then there is the artist who paints after he finishes his job as an accountant. He has to be an accountant to pay the bills because he only wants to paint what he wants, his vision. He knows he could make a living as an artist if he would paint the occasional pet portrait, but he will not because he thinks pet portraits are beneath him. Has either of these artists sold out?