Facebook is the most popular social networking site in the world, no doubt about that. But Pinterest is the favorite of the consumer–particularly the window-shopper.

Various statistics including the recently published SAP and NetBase report show that Pinterest generates four times more revenue than Twitter and increases revenue by 27 percent more per click than Facebook.

However, Zappos Labs, the research arm of online clothing site Zappos (now owned by Amazon), has been mining Pinterest sales patterns and results are not rosy.

According to the Director of Zappos Labs, Will Young, users of Pinterest would be much more likely to share a purchase than users of Twitter and Facebook, but the content shared on Pinterest generates less return than those published on Twitter and Facebook.

The report published in Bloomberg found that Zappos customers share their purchases on Pinterest more than 13 times higher than Twitter and 8 times likelier than on Facebook. But a post on Twitter generate much higher revenue – $33.66 per order than Facebook, at $2.08 an order, or Pinterest, at 75 cents an order.

“Even if a person has 100,000 followers on Pinterest and she pins something to a board called ‘Stuff I Love,’ that’s not as big a deal as an endorsement tweeted to 10,000 followers,” Young said.

It seems that the sharing of images of products do not make it so good in terms of economic return. This might scare to those who rated Pinterest as much as $1.5 billion and even more so to those who have recently invested more than $100 million in its platform, including the e-commerce portal of Japanese Rakuten, the main investor of Pinterest.

The survey, however, is contradictory if we consider other surveys, such as that made by the e-commerce website Shopify, which found that customers spending via Pinterest are 10 times higher than visitors from Twitter and Facebook. Another study by SAP and NetBase revealed that Pinterest is fastest growing social startup site ever, suppressing Facebook, Twitter, blogs and other social media resources.

The latest news from Zappos Labs is a big problem for Pinterest, because like other social giants Pinterest is hoping companies can see commercial returns from the site, so that they can monetize their platform by the large traffic they currently receive.