The Bad Leads report can be found in the Reports module in the Sales Reports section.
Using this report, you can easily find all your bad leads for a given month for a given provider. This will allow you to easily have the data needed to pass this information along to your lead providers for refund purposes.
You can search for bad leads based on the lead provider and a date range.
What date does the date filter use?
The results are filtered based on the date the lead / opportunity was received or created.