An anonymous reader writes with news that Groupon is testing out a service for letting merchants accept credit cards that could put it into competition with PayPal and Square. "Groupon's nascent payment service comes with an Apple iPod Touch, and a case that wraps around the back of the device, which allows merchants to swipe credit cards." The fee structure isn't finalized, but their aim is to be competitive with PayPal and Square. "Groupon may have flexibility to charge lower fees because it could subsidize the payments service from money it makes providing other services to merchants, they said. PayPal's service, known as PayPal Here, charges a fee of 2.7 percent of the purchase price for all types of credit and debit cards - including those issued by American Express Co.. Transaction fees for processing AmEx cards are often higher. Square charges 2.75 percent per swipe. Groupon's test service is charging a 1.8 percent transaction fee and 15 cents per transaction, Rocky Agrawal, an industry analyst, reported in a VentureBeat blog late Thursday."