I consider myself a believer of my own faith.
Am I less likely to sin? I assume you are referring to not sinning due to my religious faith.
I must be honest I haven't thought too much about ethics in my faith. There's a huge degree of theology imbedded in my ideas but my beliefs are focused on pantheism and not focused on a personal God who somehow cares about what I've done. And the term sin implies that I believe in a God who believes I can sin, which isn't implied in my faith.
In fact, when I was researching religion as a young kid I somewhat adopted the ethics of Confucianism and never really had a problem with drugs or alcohol. A few times I did rebel against my parents but I have learned to respect them. Filial piety. Of course, I don't really believe that Confucius was the one to set me straight, but I've learned that the more I get along with my parents the better my life is.
This question is not about me however, it's about all believers. My knee-jerk reaction is to say no. That atheists, agnostics, humanists are in equal footing of morality as the Christian, Muslim or Jew. The thing is, the before group doesn't even believe in sin either. So answering this question doesn't really make sense from their perception at all, in fact, it would be easier to just ask me, "Are believers less likely to do bad things?"
Which I think what's important on what is right from wrong is more important if they have certain conditions. For example, if one has had generosity given to them, they will more likely be generous themselves. For example, growing up I had my parents cable/satellite. Now I share my YouTube TV with my parents. If someone treats you with respect, you are more likely going to treat other people with respect. I am not saying that I believe in some cosmic karma, but at the same time I know everything is somewhat connected to each other.
So, if we were to apply my idea that like attracts like, dislike attracts dislike, are believers less likely to sin as a result of this?
I think I actually want to say yes to this. This is because they recognize a God that observes the sin. If they are able to understand what a sin is in their faith, even if by modern standards they've done nothing wrong - I think they are less likely to do it, especially if their religion isn't Christianity and they don't have to simply believe in Christ to go to Heaven.
TLDR Version:
Are believers less likely to sin? Yes. Are believers less likely to be bad people? No. There is already enough social conditioning and reinforcement, like "canceling" people that already does this.