The moment you decide you want to sell things to specific customers, the 'philosophy' perhaps best assumed would be that you apply your art to meet the customer.
It's like talking. We all mastered that 'art', but there is very little satisfaction (to most anyway) in getting together with a bunch of people evenings, just to assert to that gropu that you can indeed talk.
You apply your acquired skill to engage in a conversation, a meeting of people and their opinions, to the benefit of all (including yourself).
It's quite possible to consider 'Art' a noun that should only be written capitalized, and think that the best way to deal with it is to assert how well you have mastered it. Personally, i find it gets tired very, very soon to be confronted with that sort of thing.
It's like someone would get up on a soapbox and yell "Bollocks!", without allowing any of the people in the accidental audience to enquire about what would be that, and why, or express an opinion of their own, because you - the 'Art'-master - are showing them 'Art' that by its very nature is above all that.
Most 'art' doesn't do just that though, but strives to be at least a statement uttered as part of a wider conversation.
The kind of art that ends up on a gallery, or even museum, wall cannot be much more than that: a single utterance. We, visitors of that gallery or museum, can only privately take in that utterance and form a response we can share with the people next to us, but noone else. The artist can not get any response, can not know how (if at all) his utterance is received. A one way street.
Applying your skills while engaged in an active exchange with a real living human being is not selling out. It is giving the artist an opportunity to be more than just a loud voice. An opportunity to actually engage in the conversation and transform the general utterance into not just a specific statement, but even a short 'episode' out of an ongoing conversation. A real exchange of ideas, out of which new ideas come.
As always, it may turn out that you and your conversational partner do not agree to such a degree that nothing more will come of it than agreeing not to agree. Then the thing should end right there.
But it may also turn out that both you and your customer gain something from the exchange (more than just you the money, the customer something he'll like to look at).
Artistic integrity is not stubbornly insisting that you are right, that the way you did and do things is the only correct way of doing things.
Artistic integrity is admitting that your views change, that the world and people around you help you grow, and that you wouldn't do things the way you did them yesterday anyway (i.e. recognizing that if you do, you're caught in a rut, a manierism, and have lost your artistic integrity).
Or in short: it's not a bad thing to work with a client at all.