My list in no particular order.
Awful replacement wood that's poorly fit.
Poorly executed split head repairs.
Grade-3 & higher guns with the skeleton butt cut-off for a butt ugly pad installation unless documented it was ordered with a pad.
Any metal refinishing where it's obvious the polishing was done on a buffing wheel. I.E. rounded edges, removed or over buffed lettering or engraving etc.
Loose ribs or ones that some Bodger attempted to fix with some type of gum-pucky from the local hardware store.
Guns with so much drop at heel that they make the gun look like a banana.
Buggered screws.
Poorly done re-case hardening resulting in gaudy case colors.
Heavy rust & pitting.
Oil-soaked wood.
This is only a partial list, but you probably get the idea.
Then my personal subjective one is barrels over 30" in length
Threaded Mode