Amazon has worked to cultivate an image as a customer-friendly company, in part by allowing shoppers to easily return unwanted items. But the company is closing accounts and banning people for returning too many items, and committing other infractions on the site.

The e-commerce giant has a stricter return policy than many of its customers realize, and those who report “an unusual number of problems” with their orders may be prohibited from shopping on the site, The Wall Street Journal reported.

In addition to the number of returns from a customer, the bans are apparently triggered by behaviors such as returning the wrong item or items that appear used, returning technology items such as TVs or computers, or posting product reviews in exchange for compensation. Customers who have been banned are often left unaware of the reason.

“We want everyone to be able to use Amazon, but there are rare occasions where someone abuses our service over an extended period of time,” an Amazon spokesperson told the Journal. “We never take these decisions lightly, but with over 300 million customers around the world, we take action when appropriate to protect the experience for all our customers.”

Amazon offers an appeal process by which customers who believe they have been wrongfully banned can request a review of their case.

Amazon has not published a set percentage of items returned that would be deemed too high. In 2017, The Guardian published a story about a man who was banned from Amazon after he returned 37 of his 343 purchased items. In 2015, a Twitter user noted that his account was blocked after he returned 43 of 550 items.

Amazon uses an algorithm that flags customers with an unusual number of returns, at which point an Amazon employee reviews the account and makes a decision regarding a ban. The company declined to indicate how many customers have been banned for excessive returns.