As Huda said, the officers at the embassy who are assessing and doing the interviews have to have some cultural context of the person they are interviewing, not only from that country but also within the different classes of that country. Some people and some classes are more aware of the western way of living.
For example, there are things to do with how the spouse lives in Canada and the details of that. They have some context of what life in Canada looks like. Other spouses in different classes don't really....
The officer who is interviewing should have a bit of context of what constitutes a legitimate marriage in that culture, specifically. Yes, there are a lot of ways to scam the system, but the reality of the matter is that most of the cases that are deemed not credible are not decided in malice, but because the questions are a standard set of questions, yes or no.