Thought exactly the same second thought was, I bet there is a haggle session when the invoice is presented .This customer sounds very much to me as if his first language is'nt English & he's probably not a Christian but then I'm a racist . !!
Hence for this sort of client I come up with the real figure for the job double the figure & send the quote with conditions that half payment upfront.
Receive the half upfront .....Job gets done haggle over final payment proceeds I agree to a % reduction & am still quids in.