It is all a little vague. It can even vary within the same country, depending on the time period.
Let's look at the following example. You make a presentation at a conference, and you are given a bottle of wine. Its value is easy to check on the Société des alcools du Québec or the Liquor Control Board of Ontario website, for example. If you are given a bottle of wine worth $22, there is clearly no problem. If you are given a bottle of wine worth $426, it would be difficult for you to claim that is a normal expression of courtesy.
So we try to see what seems to be the practice in similar circumstances. It is very arbitrary. If the commissioner's office sends you an email saying that you can accept the gift, you are protected. So that would be the best thing to do. When in doubt, you should consult our office. You would then receive a written answer and would be protected.