Instead of looking at a supplier to decide how they 
     should rank, Panjiva looks at the people buying from 
     those suppliers. The network amongst suppliers and 
     buyers gives a much more truthful representation of what 
     a supplier is really good at building than purely 
     analyzing the suppliers themselves. 

Data is better than Marketing-speak.

The idea is that you'd probably trust the guy who actually sold 1,000 dresses to Macys more than the guy who just says they're a great dress manufacturer.

Brilliant idea, but how are they going to harvest the shipping data - I don't believe b2b trading is publicly available.

Like Apple for instance, I'm sure they have NDA's for all their suppliers. Companies probably treat this as trade secrets so competitors can't source from the same factory they are buying from.

It looks like they're using the following data sources:

U.S. Customs Import Data

Hong Kong Trade Development Council Data

DP Information Group Reports

EDDI Red Flag Database

China Export & Credit Insurance Corporation (SINOSURE) Reports

Social Accountability International Compliance Data

TriVista Sourcing Data

Worldwide Responsible Accredited Production (WRAP) Compliance Data

CUSTOMS Info Reports

They get it from publicly available US customs data, so it's limited to suppliers who ship into the US.