Is it a good practice to continuously offer staff a prize/monetary incentive to ensure that they work hard? why or why not?

Rewarding the employee with cash in terms of bonus is very good.  In this way if you set even more hard targets for the employees you will see they will surely get it.

If some one is been ignored if continously performing well then giving a token of encouragement surely makes him/her feel that if I continue there is surely recognizition and rewards.

IBut gifts every occasion  would be same as a child at home if you pamper him/her with gifts all the time not thinking if its neccessary or not then it will surely spoil the kid and to do anything he/she will ask for rewards and gifts . So do you want a stubborn, spolt child in your organization is the question to be asked to yourself.

In the short run and especially in the sales dept   prize/monetary incentives are essential to motivate the staff to higher performance. This would also help retaining good staff. But in the long run say for  a5  year  period these may not be enough to retain and motivate a tenured employee. For that the promotion avenues have to be kept open and the promotion procedure should be transparent. Empoyees  should be given feedback about why they were not selected in the current Internal Job Posting.

Monetary incentives are very good reward systems for performance, however it is only good for short term usage. If the employee thinks outside of the box and values his career's future, he might even appreciate it more if you give him certificates, plaque of appreciations, trophy awards, or things that will be of long-term usage. Since certificates, medals, trophies, and plaques can never be used up, therefore it will have more impact on their sense of self-fulfillment, like something to be proud of in the future. Instead of always giving away money incentives which will most likely be used up in a day or two.

Its good to offer incentive , but some other thing are more important than this. Give feedback - Specific, on-the-spot praise is good!  “Praise in public/criticize in private”. Use rewards that have mutual benefits, such as skill training and professional development.