Where do they get their prices? – Hopper: Flights, Hotels & Cars Review

I just searched a few flights that I have been watching. For all of them Hopper's "current lowest price" was about 20-30€ more than what I'm seeing on other sites, including directly through the airline's sites. That's a big difference considering the prices are all €100-150 each. Kinda seems hard to trust when I can already find cheaper prices than what they are offering me.
Review by Kinda Concerning on Hopper: Flights, Hotels & Cars.