haha pretty interesting question.

If I can attempt to answer this(from an online poker perspective), I would say you want to look for situations where your opponent has many hands which don't have a lot of showdown value and a limited value bet region. To put in other words your opponent is representing value betting hands which make sense but happen very infrequently, while having a lot of different combos to choose from as bluffs, so unless he is skilled enough to realize that he will be overbluffing. Of course as you play with different opponents and learn their habits you can pick up on some minor things they do when they have a weak hand (like timing tells or bet sizes) but this will differ from player to player so it's a little difficult to quantify.

Cheers.

@Julian Kopanskiy has made an awesome set of range research videos using H2N which is somewhat relevant to this. I would recommend checking them out.

Imo, betsizing can be a huge tell once you know different players tendencies.

I find that it's generally when someone plays a hand in a way that's outside of the norm. Stuff like checking back the turn and then overbetting the river or check raising the river when you don't think that your opponent would check a value hand to begin with. Bet sizing tells can also be huge versus recreational players.