In live games I usually deliberately give off different tells to fux with my opponents minds, im mostly what youd call a math player though. Its not really "math instincts" as you say, its more calculations and estimations.

That being said, yes, "bad" players give off tells that I pick up on. By watching how people act before their turn you can often have some insight into what they will do.

The problem with relying on tells too much is the following: Knowing your opponent is only moderately strong doesnt give you correct odds to hit your partial outs.