The reward has to be good enough, as far as your dog is concerned.
As a long time positive dog trainer I know all too well how powerful a good reward is to a dog. That is, if the reward is something that the dog desires. Not all dogs are motivated by food; some are motivated by a ball, frisbee, tug toy or favorite stuffed toy. The secret to rewarding a behavior is to offer your dog something worth working for. Food tends to be the "go to" reward; and if it works then it is easy to carry around. That said, there is a big difference in the value of each food reward. If a food does not have enough value, it's not going to work. Too much value and your dog is not even going to be able to think.
Reward - something given or received in return or recompense for service, merit
Watching your dog's behavior closely will let you know how the reward is working. Many times we have had to downgrade to a lower value item of food when training. It all depends on the dog; that is the most important thing to remember.
Tilley loved food but she was also a timid girl and would become more so in the presence of strangers. Food rewards worked great when we were alone; at home or even out in a park but not around a lot of people that she didn't know. But, if I pulled out a ball or frisbee, that all changed; she became Miss Outgoing and worked for the catch. It was truly an amazing tool for transforming her very state of being in certain situations. This worked so amazingly because Tilley loved nothing more than catching. Food was great but in high stress situations (which is different for every dog, blog later this week) it was not enough to pull her out. With a ball in hand Tilley became someone else; a dog that many people didn't even recognize as the timid little demur girl they had come to know.
When using a reward system to teach a dog; you must use an appropriate level of reward. That means that if you are teaching a new behavior in your living room and there are no distractions then use the least value treat. You want to make sure that it has enough value that your dog will work for it; but don't use over valued items. You need to save high value rewards for the really hard stuff Your dog may work for cheerios in the house but not out of the house. If you are using food rewards then you should have a variety of different value level rewards at hand.
If you are using a toy of some sort; whether it is a ball, tug toy, stuffed or disc; you need a variety as well. Variety in toy rewards can be achieved by the use of different items which hold a variance of value levels; or it can be a difference in the use of one item. Elsa's very favorite toy is her squeaky kong ball; she will literally do anything for one. A low level reward with the ball could simply be passing it to her; allowing her to take it into her mouth. Higher would be a small toss in the air; higher reward would be a bounce catch. The highest for her would be a distance toss of the ball.
Rewards are powerful; it is amazing how quickly a dog can learn when rewarded. But with reward comes control; you cannot dish out rewards willy nilly style. You must use them according; if you overuse them you will actually diminish your training results. Rewards are used to teach, proof and be weaned off quickly. Depending on the behavior will factor in how long you keep the reward system around. I consider some behaviors, like the "come" as extended high reward ones. Again it all depends on the dog, the behavior and the environmental situation.
Rewards are just that, a reward for a behavior accomplished successfully. Rewards are not bribes. You can use a low level reward to assist in a maneuver if needed but, it is very quickly removed as the object to follow. There is a great deal to know about properly training; it is easy to make huge mistakes that can take a great deal of work to undo. In dog training, less is more. Less words, less movement and less rewards. Save the greatest payoff in rewards for the phenomenal stuff.