insta-checks from players after cold-calling PF?

I tend to believe these are very polarized, either a lot of strength (omg check fast) or air (omg I have nothing).

insta-check-call or just insta-call. Typically a hand the player knew immediately was not worth a raise or a fold. This could differ from opponent to opponent but it's like 99 on a Q72 board or a weak TP type hand.