On the other hand, it's the customer's decision to put Cloudflare in the stack. They have decided to put Cloudflare on the path, just as they would have decided to use nginx. There really is no one to blame (because the end here is not the customer's server, it's the cloudflare server) and if you really want to, you should blame the customer.

EDIT: just read your answer below, my comment is off-topic. Sorry.