I am not sure what you mean by 'verify'.
What I would do is:
1) print the parameters on the report (this will allow to visually ensure that they are correct)
2) if you have a filter for the data, I would display the different parts(each line of a nested 'if statement') and display that in the details
3) keep building up the logic and what you display until you a) you find your error or b)you run out of things to test (hopefully a comes first ;) )
If the data is coming from a stored proc or view, verify that it is returning the correct data by using the displayed parameters.
HTH