How to cancel this job?

[KristineS]

The consensus seems to be to walk away and that's what I'd advise too. Life is too short to work for people who are rude and nitpick and nickel and dime you over everything. Just make sure that you are clear as to why you're walking away and can explain if they make a fuss which comes to the ears of other customers or potential customers.

[CCAdamson]

Assuming you are not bound contractually to perform any type of work for them I would tell them thank you for the past business but I will not longer be your service provider. They will apologize and beg you to stay as they have in the past but this time you need to just stand firm. It isn't worth the hassle.