River Value Bet

[GTSamIAm]

When you're playing against passive players how do river value bets affect your image? Even loose guys will sometimes tighten up. Or some tight guys will temporarily loosen up when they think they're being pushed around.

I've read somewhere before, probably here, that restraining from using a river value bet and letting fish see your cards for free encourages them to play loosely in the future. Some people just take the game personally, I guess. What do other people think about this subject? As a general rule, is it true?