NEW YORK, June 22 (Reuters Breakingviews) – Amazon.com’s (AMZN.O) Prime service is a club that’s hard to quit – literally. Competition cop Lina Khan filed a complaint on Wednesday alleging that the e-commerce giant enrolled U.S. customers in its subscription product unwittingly and made cancellation unlawfully difficult. When it comes to sharp sales practices, other companies have done worse, but the Amazon case could still hurt. Under Khan, the Federal Trade Commission has gone after “dark patterns,” user interfaces that trick customers into unwanted purchases that are difficult to cancel or refund. The FTC has leveled similar charges at others too, including video-game platform Epic Games. For Amazon, the case targets the core of a $1.3 trillion business. Citigroup analysts estimate that Prime subscribers spend up to 2.5 times more than non-subscribers on Amazon’s marketplace. That extra spending matters: Amazon’s North America segment recorded a razor-thin operating profit margin of 1.2% last quarter. With 80% of U.S. households already subscribed, retention is king. Amazon executives dubbed their cancellation process “Iliad,” the FTC claims, after the Greek epic on the lengthy Trojan War. There’s a more recent historical comparison: Wells Fargo (WFC.N). That U.S. lender crossed a different line, with employees forging signatures to open unauthorized accounts, earning the bank billions of dollars in fines and other harsh punishments from regulators. Amazon isn’t accused of anything so devious. But the principle that consumers deserve a clear view of what they’re getting into, and how to get out, shouldn’t be a stretch for a company built on making customers’ lives easier.