This seems like an odd question for an artist. Most of us need money- rather desperately.
I have and have regretted all of them except one- the clients daughter posed for me and I directed the entire painting. The clients were extremely happy. The others were done from photographs- as the clients were too busy and refused to sit. I consider these commercial- not fine art. They looked like what they were- fairly competent copies of photographs. They never went beyond the surface of the photoprint.
What to do about commissions then? It depends on why you have decided to be an artist in the first place. Is the money more important than the images you personally would paint? Do you care what you paint and do not mind being in fact, a hired brush. If you were to be a portrait artist today you would almost be certain to have to paint it from a photograph leading to results like the very unfortunate Bill and Melinda Gates portrait justifiably panned by Blake Gopnik in the Daily beast.
I do not want to post it here as it is quite dreadful. The artist was given one hour with the Gates.
The last great presidential portrait- that could stand alone as a work of art was the J.S. Sargent portrait of Theodore Roosevelt. http://en.wikipedia.org/wiki/File:TRSargent.jpg
The rest are simply historical paintings of no great value except for the prominence of the sitter. President Clinton's portrait is insipid and Mrs. Clinton looks like Howdy Doody.
If you are stirred to do ego paintings of prominent or wealthy sitters- do so- but the importance of the sitters will far outweigh any value you add as a painter. I have not seen any examples that contradict this. If this is your idea of what you think fine art is- by all means do it. You will not be alone as legions of contemporary 'portrait artists' are doing the same.
I have done some quickies to survive- but I try NOT to sign them or make an unintelligible cartouche at the bottom.
I think from the beginning of your career as an artist you have to decide what is the most valuable thing about painting. What is it you want to say? What moves you. What, most importantly do you love? There will be times when you are desperate financially and have to paint things you would rather not- but is this what you wanted to show for your lifes work? I cannot give anyone the answer. Read biographies of past and present artists you admire to get some iseas or guidance. There will some bright lights along the way- clients who will actually sit that you would love to paint.
I have had many chances to paint polititians and other wealthy people but I won't because there is no way in hell I would be able to make a painting- a rendering yes, but I value myself and my short time on this earth too much to do this. I would rather bag groceries.
I have always wanted to make pictures- my own in the best way, with the best craftsmanship I could muster. There are some brilliant painters working this way- and strictly from life. These are the painters to be reckoned with. The rest are all wannabees.
This is what Steven Assael has to say about painting from life.
"His paintings have been called Post-Post Modern and works strictly from live models. Arlene Raven describes him as wanting "the greater possibilities of duration. More variety, and a broader range of values and colors, a chronicle of the transformations of changing light, spent over real minutes and hours with his model." In speaking of his work and how it contributes to contemporary art, Assael stated that, "Even though art is dead as we have known it, painting is not." 
And as I have said how you paint is your business, this blog is about how I paint.