Yes, those do seem to be the top 3, but they don't always go against people. On the Facebook group if you put age gap into the search bar you can see quite a few couples where the woman was significantly older and they were approved. One woman named Vicki sponsored a husband from Ghana. She only met him 6 months before they were married and she is 19 years older than him. I have read a lot about Habibti on here, but there is also another woman that applied in Rabat who was 12 years older (not as big of age difference as Habibti) than her husband, they didn't have a wedding and had different cultural backgrounds - they were approved by CIC. It just goes to prove that the visa officers approve/deny whoever they want and it doesn't seem to be based on any points method by the CIC.
I don't have any of those red flags, but there are other ones too. A lot of people get turned down for not having enough visits before/after the wedding, not having a good job (say you are doing it for economic reasons), not speaking English well (say you can't have good communication), not having both sides of the family at the wedding. One poor guy from India was turned down because he didn't have his photographer take a picture of a part of the wedding ceremony that, I guess, is a big deal in their culture. He had witnesses to say that he did have it at his wedding, but they just didn't have pictures of it - was the only thing listed in his refusal. He was going to have another wedding and take pictures of it this time and reapply - that is just sad!
I think CIC should have a fairer way of approving and rejecting applications that just isn't based on one visa officer's personal biases. It could also be quotas, I guess, maybe they are stricter about who they want to put through if they have a lot of applications and weed out any couple that is not perfect. It is very easy to see looking on this forum and Facebook that some people are approved with almost identical red flags that other couples are being rejected for. That's why I think there is no way to predict what is going to happen with a lot of people's applications.
Couples just have to give it their best shot and hope for the best. If rejected, most spousal appeal cases seem to be approved. Fair or not - CIC has the last word, unless you appeal it.