We stand by our verification methodologies because we use multiple techniques simultaneously that give us a complete picture of each email.
However, you may notice bounces even when sending an email to a valid address (extensively discussed across various blog posts here). Some reasons include:
Deliverability issues (email gateway sends you a 'fake bounce')
Time decay (time elapsed between the time of verification and send)
If you believe that our platform is not meeting its advertised SLA for validity, you can submit a support ticket with the email addresses concerned. We will look up the original results in the system, run another verification to find any differences, and then send emails from multiple email infrastructures to see if they receive bounces as well. If you are still unsatisfied with the response, we will give you your money back, up to $20, which we consider a sufficient sample size to test the platform with (this does not apply to those using one of our Free Credit offers).