I find that to be true the more I read various threads. I also found the whole process of getting married to my husband there was almost a no-go for the same reason. I got the impression that because I was married and divorced before that they had in their mind that our relationship was a sham from the start and then sought out to look for any reason to not let us marry and to make the whole process as painful as possible. It wasn't until I paid a huge sum of money to the reviewer and called in a favour for her husband (long story) that the wedding was allowed to go through. This is also why I don't hold out much hope they will approve his application for PR without an appeal but I guess eventually I'll find out if I'm right.
Some of the reasons they approve and reject people are so bewildering. One couple was denied because the husband didn't speak good English and the visa officer assumed they couldn't have good communication, so therefore it couldn't be considered a genuine marriage. Another couple was turned down because the husband didn't have a good job and they said he had economic gain to come to Canada, so therefore they didn't consider it a genuine marriage. Then another couple was denied because the husband spoke good English and had a good job - the visa officer said that because he could work anywhere in Canada and had no language barriers he didn't have to stay with her and they felt he would leave her once he arrived in Canada.
I have seen posts where in the rejection letters some of the reasons couples were denied was because people (guests, not the couple) were not smiling enough in the wedding pictures. Another rejection, where the brother was wearing a suit jacket and jeans to the wedding, so that proved it was a sham marriage. Quite a few couples were denied because the spouse could not afford to fly relatives from Canada to come to the wedding. On the other hand, there are couples that don't even have a wedding that are approved.
They are couples who have been denied because their marriages were registered too quickly and then other couples who were denied because they knew one another for years before registering their marriage, and the visa officer said because they led separate lives for so long they were not considered a genuine marriage as they were not emotionally tied to one another or they would have registered their marriage sooner.
There are couples who are denied because they don't have the same culture and/or religious beliefs, then there are couples where the wife converted even before the marriage, and the visa officer said that she only converted because she thought it would help when she applied for spousal sponsorship so it was a sham marriage.
As far as being married before, there was a woman that was in the Facebook spousal sponsorship group that sponsored a spouse before and divorced him (not sure how long they were married), and then she applied to sponsor another spouse and was approved. There are also a lot of couples on here that are rejected when neither partner has been married before.
I am completely at a loss to see what formula they use to decide who to approve and who to reject - looks to me like it has to do with luck and the quotas the visa office has to fill at the time they are looking at your application.