Dotcom Distribution, an e-commerce logistics and fulfillment company, looked at the 11 biggest flash sale sites — such as Gilt, Fab, RueLaLa, etc. — and ranked them by customer complaints on Facebook.

The company found nearly half of Facebook comments about these brands was negative, and of those the biggest complaint was shipping.

The good news: Fab.com had the lowest percentage of negative customer comments.

The bad: 61% of Zuliliy's Facebook comments were complaints about the company.

Here's a detailed breakdown of who's winning and who's losing the flash sales battle on Facebook. (It's also worth bearing mind that some of these brands are clients of Dotcom, and some are not.)

The problem for flash sale sites on Facebook is that the companies need the referral traffic that Facebook generates, but customer complaints can be very public.

Shipping is the biggest issue.

Fab.com has the lowest rate of complaints about shipping. Zulilly, HauteLook and Beyond the Rack have the highest rate of complaints.

Surprisingly, logins are a barrier to shoppers, not a help.

The Foundry has the worst reputation when it comes customers who believes its marketing is misleading.

The Foundry has got some work to do on customer service, too.

Fab.com's website has the largest rate of complaints.

Gilt gets the most complaints related to product.

Here's Dotcom Distribution's advice.

And more ...

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