Sites like Flipfilter provide some awesome stats on marketplaces - four marketplaces in Flipfilter's case.
The majority of his stats come, understandably, from Flippa. He has an API access to certain sections of the Flippa's database and draws his figures and information from there.
However, such API access offers very restricted views. For one, you wouldn't get to see all figures, just the figures Flippa choose to share with you. There would also be restrictions on how you use those figures. For example, you wouldn't be allowed to use them in a way that Flippa doesn't approve. If there's data or stats that's useful to buyers or sellers but not helpful to Flippa, you might have to avoid disclosing them.
What stats/information from Flippa would you find useful over and above that provided by the Flippa search feature? There's a good reason I'm asking, it might be possible to arrange to get that data.
All listings that have been suspended.
All sellers who have been suspended / banned.
A list of sites that are publicly showing as sold but where the sale has fallen through or there's a non-paying buyer.
Comments that have been removed from listing threads.
All listings where the BIN is less than/more than 12x monthly profit...
I don't know. As a seller, as a buyer ... what would you find useful?