It doesn't matter if the painting is his profession or not. If he promised to do it, it is in the contract and he has to do it.
LZ said he doesn't care about paying that $100. What he wanted is to finish painting the ceiling like it was before. Why do you think it is fair for him that the contractor didn't do it right? LZ wasted his time and energy too only to get this unfinished ugly ceiling? I don't think it is fair for LZ. I think it is very fair to complain about this contractor, and this contractor happens to be a Chinese.
The contractor lied about that he will painting the ceiling. I think he probably implied that he will paint the ceiling like what it looks like before. If he told LZ what he will do, I don't think LZ would agree in the first place.
你真的不能写中文吗?