During testing, there are areas you need to be sure are covered before you are sure you found a bug:
- technology (are you sure you are understanding the technology behind the AUT - how stuff works)
- tools (are you using the tools the right way, is everything set up correctly)
- business logic (are you sure you understand what is the app supposed to do)
- testing skills (maybe your testing skills are up to the challenge)
- individual factors (are you focused, well-fed and rested and such)
What are the strategies to mitigate false positives? Or, how to be sure you found a bug?