Can I incentivize my users to complete a survey?
Yes, you can incentivize your users however you want in order to complete a survey.
How do I know how much I will earn upfront in order to prompt mu users accordingly?
You can listen to Pollfish listeners/notifications as described in the Documentation and see how much you will earn upfront before notifying the user. All prices are in USD cents.
How do I know if a user completed a survey?
There are several ways in order to track this. You can listen for relevant listeners/notifications as described in the Documentation. Moreover you can also set up a Server-to-Server postback call or just track them on your app's page on Pollfish Developer Dashboard ("Completed Surveys").
How to I implement incentivization in code, do you have any example?
You can read more in detail (and with examples in code) on how to implement the rewarded approach in the following link.