In a sense what you're suggesting makes sense, but.................if you raise negative issues when selling a service you might struggle to sell that service.
There ARE potential problems, but training before you start will help you avoid most if not all of these.
I'm sure some will disagree, but if someone came to carry out work at my home and presented me with disclaimer forms I might doubt their credibility / experience and not take them on.
Unless, of course, there was a known potential problem with a particular item.
Thing is, as a service provider you will be expected to be capable of dealing with such problems or decline to take on the job as you would be unable to offer assurances / guarantees.