To bet or not to bet
The tote board is a random self organizing system that comes alive as it channels the crowd's energy, armed with knowledge of the Fair Odds (after the racetrack takeout) for each horse in the race; horses offering overlaid odds are readily identified.
The tote board is alive
Playing overlays is the name of the game and it's a dynamic process, the tote board is alive right up until the start of the race and even while the race is running as the on-line wagers are closed, accounted for and aggregated to the pool. Thus in order to be as certain as possible about the price of an overlay on the tote board, horse players should place wagers as late as possible, one or two minutes prior to post time.
Due to the late action on the tote board, at times an overlay will be borderline and may not end up as an overlay. If there's any chance the odds will come down to the point where your WIN ticket will not be a play on overlay, it is best to either abandon the play in favor of another "possible overlay" or pass.
Also keep in mind that a favorite can go beyond the wager bifurccation point in the same way. Likewise, if there is a chance that a play might go beyond the bifurcation point after you purchase the ticket, then it's better to pass the race; one should not force it and hope for the best, there are too many races. Strike rate, strike rate, strike rate, when in doubt pass the race; keeping a higher strike rate will maximize long term profit.