Live NL game question

[Ed S.]

How does one approach a live NL game where most of the players are underbetting their hands,wether its a made hand, drawing hand, marginal hand ect... Say for example after a pre flop raise of 20 bucks you get 3 callers and there is 67 dollars in the pot and the flop is Ah 7s 10s and they(preflop raiser) or anyone else for that matter, lead for like 20 bucks. How does one approach a game where the pot is not correctly being bet with 90% of the players at the table?

Ed S.