I think the "self-selection" comment was referring to the businesses, not the customers. An analogy is those "customer forums" that many companies setup, thinking, "Customers can support themselves!" but then realize that it's more about "Customers can learn how crap our company is!" and they take it down. So, crappy businesses won't want your service.

But even a well-run business will be cautious about letting some random internet stranger post comments to their homepage. You need to make sure that comments aren't from competitors, people don't post multiple times and most importantly: That the company can respond to criticisms.