Lots of players will try to make a defensive bet in this situation, say $5, in an effort to keep their opponent from betting more than that. If you don’t think you have the best hand, and you’re not willing to bluff, don’t put any more chips into the pot. If you are not willing to bet at least what you bet in the last round ($10), then you should probably just check. The turn is a scare card which causes you to doubt whether you still have the best hand. Let’s say in a $1/2 cash game, you raise to $7 preflop and then bet $10 on the flop.
When you bet you generally don’t want to send out any signs of weakness, but one common mistake a lot of players make is to reduce the size of their bets in the later rounds (turn and/or river) when they’re lacking confidence in their hand.
