Here's the closest I can find to legal info on an official website, looks to be from ~2006 or so.
Unofficial ENG translation here: http://www.asianlii.org/cn/legis/cen/laws/mfaoesoi533/
Hey Max, will you post an update to let us know which solution worked? Encountered this a few times recently; curious about this 98% fix.
I think all the comments in this thread are right on the money; I learned the hard way that paying for my time is NOT the same as paying for my expertise. Another suggestion I have is for them to bring a really clear list of what they're looking for in a template to you ~in writing~ and you make that part of a Mutual Agreement; it's not always airtight but I strongly suggest you get something in writing, especially when offering "options" for their design.
Looks like results from Moz, Litmus, Hubspot, and several other "known" companies pop up. Take a gander, maybe a friendly infographic is what your client needs to get them on board with best practices.