So, let's pretend you're a pool-slide salesman. Say someone has a pool in their backyard. This pool isn't very deep. Now say they buy a used slide from someone else (not you) and install it. Then they call you up asking for replacement parts for their slide. Then later on someone is injured while using this slide, because they installed a slide in a shallow pool and people were using the slide incorrectly. Whose fault is it? If you said "mine!" you're right, according to the Ontario courts.
You read that correctly: the store that sold PARTS for the slide, but not the slide itself, was held 80% liable for the tragic accident that paralysed a 15 year-old girl. The girl was held 20% liable because she slid down in a crouched position, despite her mother telling her to slide down "on her bum".
A link to the Ontario Appeals Court judgement is here. In it the judge notes that the trial found that in several cases the pool owner asked if it was "okay" to install the slide or if there would be any problems. Several people at the pool store told her there would be no problems. He also notes that the instruction label on the slide had become faded and worn, which is not surprising considering that the slide was purchased used and was over 15 years old.
These factors aside, the judge's decision to hold the pool store liable was based on the fact that the woman who bought the slide trusted the pool store staff to provide safety instructions regarding the use of the slide. According to the judge, it's not obvious that slides pose a danger, and so when the pool store staff said "no problem" about installing the slide, what they should have said was "no problem but always go down feet first or you may be paralysed". Despite the fact that she didn't specifically ask for any safety advice, the court found that it should have been obvious that safety was her only concern, so the store staff should have advised her as to the pertinent safety rules.
What this means is that anyone who is potentially an expert on any topic is liable for the accidents that befall others. If a court feels you represent yourself as an expert in some capacity, and a person asks you for advice, you are legally responsible for the advice you give. Thus a pool store is responsible for advising anyone who asks a safety question; if they answer the question they are now responsible for anything that happens as a result of that answer.
The legal test mentioned in the decision is the "but for" test. "But for" the advice given to the woman, she wouldn't have bought the slide. That is, if the pool staff had said "don't buy the slide", or "don't install it", she wouldn't have installed the slide, and thus her daughter wouldn't have been injured. This, combined with the fact that the woman trusted the pool store staff as experts, means that the store is responsible for any injuries that result on account of their "advice".
I guess if you work in any industry where there is even the remotest possibility that you will advise someone in some aspect where there is some safety factor, you'd better have lots of insurance, or else just keep your mouth shut.