How do you know if a backpack is good quality?

So, I'm in the market for a new backpack and I'm wondering, how do you actually know if it's good quality? Are there certain materials I should be looking for? Do the zippers and stitching matter? Is it all just about brand name or are there other factors to consider? I'd really appreciate some guidance on how to make sure I'm getting my money's worth when it comes to backpacks.