I go mostly by feel, but nowadays with all the finishings they put on the fabrics in manufacturing, it is more difficult for me. Secondly, I hold it up to the light. If I can see through it, I know it's not a good quality. It took me a little time to be able to judge a fabric. I also look at who manufactured the fabric as some manufacturers are known for better quality fabrics, but they are more expensive as you would expect. But in the end, whether or not a fabric is "a good fabric" depends on what I am going to use it for. If I need a novelty fabric and it is only printed on a poorer quality fabric, I use it. It's good for what I need. If I'm doing a quilt that I want to last for many years, I search for and buy the best quality quilting fabric I can find no matter how expensive. If I'm making a quilt for my dog, I use the cheapest decorating fabric as he doesn't care what he gets.
Good quality quilting fabrics have gotten pretty expensive in my opinion. It is not uncommon for me to see fabric for sale at $13 a yard where I live. But an expensive fabric may not be any better than a less expensive one. Sometimes I think the expense reflects who the designer is.