I have two takes on this.
A place i used to work was always a little nervous when they were the low bidder. they always figured that they had left something out.
OTOH, a competitor of ours was able to underbid us by 20% on every job we went up against them on. Years later their chief engineer came to work for a successor company of the one I had worked for and we used to chat now and then. I am not real sure to this day how they pulled it off, but the projects they underbid us on made them money, and he got some really nice bonuses for the projects.
At the time, none of us could figure out just how they pulled it off, and even now I am not real sure how they managed it.
Of course their last project was a real corker. I think the owner died in the middle of it, and it was real downhill from there. the employees bought the company but just didn't have the skills to make a go of it with the owner gone.