Thanks @georgontech for the answer. And it is better to implement what is said by @onealfa I agree with him. Also remember what I have said those who are not sincere in their upvote exchange, you can block them not all or randomly. Now I face the problem. If it continue, people will leave the system. Suppose I upvote you and receive UC and use them, after that I gave you negative vote then your post value will decrees. So what will do or say, if it happen with you. Just imagine in my place and for the system. Thanks you again.