Large number of buyers/sellers from across the globe. So visibility that one gets by listing say a website on Flippa is far greater than other portals in this niche. Also key statistics like Google Analytics data and transactions through Stripe and PayPal are verified and buyers can gauge the same right from the listing.
High fee. They charge 49$ + 10% success fee for starter websites. Even after that, PayPal or Escrow will further add to the charges. Lots of scammers. So at times, someone will press Buy Now button only to not respond. This will cause delay leading to relisting (although no extra fee will be charged in such scenario). Flippa perhaps need to place fund of buyers under its control and then let anyone press buy button.
I am often looking for buying a premium domain or starter website that is AdSense approved. For that, I occasionally visit Flippa.
Flippa is the primary clearinghouse for available domains and ready-to-use web sites. It is interesting that they are now a platform for buying and selling newsletters as well.
There are a lot of sites that are created specifically just to flip and it is hard to differentiate between sites/domains with value and those that are just cookie-cutter duplicates.
Flippa serves the purpose of being a comprehensive clearing house of domain names, web sites for sale, and newsletters