Maybe I have been lucky over the years, but most of my girlfriends are good cock suckers and most will swallow.
I lived with one who was a champ at sucking cock and always allowed CIM, but she would spit. I really didn't care what she did with the cum afterwards. Truth be told, I think she didn't swallow because she was a fanatic about counting calories and as such, cum was just needless dessert.
I've even dated women who were LOUSY at sucking cock, but they would still swallow.
A woman who refused to suck cock to completion would be a deal breaker - I'd walk.
I'll tolerate a woman who spits.
I expect her to swallow.
In my experience, women who are right into cock, who love to play with it, analyze it, and tell you how beautiful it is are the best cocksuckers. Those who sort of just figure it is what it is - meh - they will be lousy in bed.
Nothing beats a woman who loves cock. The look, the feel, how it responds, etc. They are out there and they are the keepers.