Grass fed beef often has a gamey taste or, worse, fishy!!! If I want a fishy taste, I'll buy bad fish, thank you very much! :) I think it can also depend on what kind of grass the cow has fed on.
I think there are cooking methods to help with the taste, but I'm not sure what they are. I buy organic beef from a local farmer and they use grain to "finish" their beef. Thankfully, they use organic, non GMO grain. It's more expensive, but less expensive than buying grass fed and having my family hate it and need to throw it away. That has happened to us before, it's awful, isn't it?
One of the great benefits of grassfed beef is the high content of Omega 3 fatty acids, which is actually higher than salmon! It's so very good for you, which makes it so sad that it tastes so funky.