Where in the world, would someone ask for "illegal" work???
Does bitcoin have a reputation, to generate money from illegal operations? {Thank you Silkroad}
No matter, what you say, all bitcoin transactions can be traced. No mixer can help you hide your coins.
I watched a video last night, {will post it} on a meeting held in USA, where they discussed "Anonymity" and the expert said, do not think, any anonymity is currently possible with bitcoin. {Check youtube - Speaker was Kristov Atlas at a Austin Bitcoin meetup}
So gain your bitcoins legally and enjoy your income. To try and hide from {Tax / law} is not worth it.