If no one sees, reads, or hears your work, does it really exist? If you're pure but unpublished, not shown and unseen, are you really a creative, or just a hobbyist?
Unless you are independently wealthy, or have a kindly contact who will exhibit your work unadulterated you will sell out. As soon as you are hired by a client, or enter a competition, you are subject to someone else's requirements. Your work is edited, manipulated to demand, it has to fulfil a brief. But don't dismiss writing a jingle for a car sales chain, it could pay for your pure 'personal work'.
But there are degrees of course. And if you've dined out on your eco credentials, perhaps that car jingle is best avoided. The question is to know when to sell out. If there is a principle to which you hold dear, draw up your red lines and make them known, and seek out like-minded organisations. And find out how much cash they have. If they're skint you can park this passion in the 'personal work' folder. If you have more red lines than a Spirograph then you should probably seek a second job to fund your purity.
But happily working for the arts council, a magazine or creating a graphic for a local firm rarely crosses many rubicons. But they might have a different idea of 'good' than you. I tell every wedding couple I photograph that I will not 'Schindler' their pictures- you know that garish 'oh-look-it's-black-and-white-apart-from-the-rose-which-is-ridiculously-red' – thankfully my couples have been reassured rather than dismayed, but you never know until you state it.
And if your client insists on violating your aesthetic red line, then you have to ask how important it is to you. And If you are the right person for the job. You should probably turn it down, or at least make sure no one knows you did it. But if your potential client dresses up their hum-drum job as a 'great opportunity' for 'portfolio expansion', it's probably short hand for fleecing you.
There aren't that many gallery spaces, or other options for 'purity', but merely having to complete a job in a different way to you originally conceived isn't selling out, whatever your fundamentalist friends say. That's just called working with people, building your reputation and getting your work known beyond the fridge door. My best work has been done for other people, and it's more satisfying because it's had a purpose beyond mere 'self abuse'. So sell out early, sell out often.