We've seen a few cases where the tiler (and plumber on our plumbing forum and sparky on our sparky forum) has lost a case because he shouldn't have done something but the customer said do it. The court see you as the expert, a third-party expert witness they get in to take advice from would say hands down that you shouldn't have done whatever it is if you knew it would fail.
If it isn't acceptable due to safety, the customer signing something is worth jack. You'd be better off not signing anything and denying you even spoke to the customer let alone did the job. (Not that I'm condoning that!)
If it isn't acceptable due to safety, the customer signing something is worth jack. You'd be better off not signing anything and denying you even spoke to the customer let alone did the job. (Not that I'm condoning that!)