what stakes do you play? at 25 or 50NL there are lot of guys who never heard of pot odds and who can´t be pushed off giving the wrong odds. bet at least the pot and make them do a mistake calling. if they hit, so be it and try to get a cheap showdown.

in a heads up pot u should bet close to pot sized too. it´s not only about giving him the wrong odds, but if he´s not sitting on a flush draw (what he is more than 75% of the time) and the flush draw completes on 4th or 5th street it would end the betting for u.