Parents have a HUGE impact on what their kids think. I value my mother's opinion and I'm very close with her so when she tells me something, I usually listen. I've had plently of relationships where my mother would be nice to my boyfriend's face but not so nice behind his back. Although I didn't break it off right away, she definitely put thoughts in the back of my head that I never had before.
It's been much easier now that I've gone away to school.
I've just learned to listen to everything my mother says but just take it as her opinion and nothing more. I also go to my Aunt or my sister for a second opinion. If they're all saying the same thing, I then revaluate my relationship. My Aunt and my sister usually are as objective as my mother.
Luckily, my mother loves the guy I'm with now.