Look for the steel used. If it says only "stainless" or "surgical stainless", it's low-end stuff. If a company is using quality steel, they'll probably advertise exactly what it is. Some dealers, like AG Russell, list the steel type in every product description.
Check for side-to-side blade play when the knife is open. That's a big one for me.
Look closely at the "fit and finish." Look for gaps, parts that aren't lined up quite right, sloppy work, etc. Here's a good comparison photo displaying fit and finish. Which one would you prefer?
"Walk and talk." Does the knife open smoothly or does it feel gritty, rough, or too tight or loose? On locking folders, the lock should engage with a crisp 'snap'.
Don't judge a knife by it's brand, price, or country of origin.
Hope this helps. Not a complete criteria list by any means, but I think it'll be a good start for you.
Best Wishes,
-Bob