What do you guys think about value betting when you aren't sure if you are ahead?

I've read in a HE book (Sklansky, I think) about betting for value when you are unsure if you are ahead, but think it's possible that your hand could stand up, or you could hit another out. Particularly with this player is weak, you get value by pumping a pot that they'll likely call down with 2nd pair, or top pair with weak kick.

I often get antsy betting on the river with, say top pair-mid kicker after I flop top pair, bet, and encounter a re-raise or strong call from an avg/weak player. I think he's increased is EV by getting me to check down to the end, and could buy a card from me. What I've been trying to do is if we both check on the turn, and the river is a blank, I'll bet out for value on the river to try and get a crying call.

I know it depends, but is this a flawed approach? Maybe this IS value betting?