There's way too much video of skilled fellatixes in action for any woman who truly cares about either making a lot of money or making people happy to not learn how to give a good blowjob. (Why do we say "give a blowjob" when they are always sold? But I digress.) As to the feedback question, +1 to the above; I'd add that some guys may not be good at, or enjoy, giving feedback, or the may just be so happy to find their dick in someone's mouth that they just don't care.
But I'd also suggest that a woman who cares about what she's doing can ask the guy if he likes what she's doing and if he rather have something else done.