At unibet where I play, at 10NL, there are people who simply downplay everything, no matter how big they hit. So if they limp in and the flop gives KK, and they check, they could be holding J5 (=nothing) or KK (=quads).

Here's an example:
Guy is holding TT, he limps in on 2BB, 3 people in the pot. The flop gives him his set and one overcard. He checks, another guy holding 22 raises 3BB, he calls. Turn is a 2. He checks, opp raises again 3BB, he calls. River is a blank. He check, opp checks. He wins the 19BB pot with trip 10s vs trip 2s.

My question: what is the best way to play against people like that? I mean, if he calls a raise, he can have anything really. The only way to potentially get a read on his hand would be to "see how high of a raise he will call".