Gaps (parts not being flush when they should), poor alignment and fit, off center blades, warped blades/scales/etc, poor machining, bad hardware, blade play in any direction when open or closed for folding knives, unchamfered/unrounded edges etc.
Anything that's handmade that I can immediately tell is handmade (in a bad way), or anything that's machined that doesn't have the precision I would expect (also in a bad way). The pinnacle of knife craftsmanship are handmade knives that could pass for being machine made - they're just that perfect. Knives that are largely machine manufactured can be good too, but they'd better be mechanically perfect.
All of this should come before any design choices, or things like finishing (colors, materials, coating, etc). I'd rather buy a well made tip-down carry, assisted, serrated, black-coated tanto knife from China than a a knife without any of those things but with poorly manufactured and fit parts made in the USA. Not that I'd actually buy either of those.