Calling bluffs with weakish hands.

[SeanC]

Hey,

I'm having trouble profitably calling bluffs/very thin v-bets with weakish hands like MP or TPWK. Not that this is something one should be regularly doing, but I feel my folding tendencies are kinda -EV.

My first question is regarding the math. If I'm getting, let's say, 3-1, do I need to feel there's a 25% chance he's bluffing to call, or deduce that he would bluff with ~25% of his "betting range" (a missed draw or two, for example), which itself may only be 50% of his overall range...therefore meaning he would only need to be bluffing ~12% of the time (.25*.5) for the call to be profitable?

My second question is how do you accurately quantify the likelihood of the person bluffing with certain holdings of his range? Intuition and history? That's obviously the tough part but are there any tips or tricks to be shared?

Thanks.