The North American arm of Amazon has increased the momentum behind its controversial trade-in strategy by offering an extra cash incentive to those willing to send their old games to the online retailer.

Joystiq reports that Amazon will until the end of August offer an additional $30 credit to punters willing to post off $60 worth of games – and it’s a deal that’s being heavily promoted on the retailer’s website.

Amazon launched its pre-owned scheme in March this year, though High Street rival GameStop quickly moved to belittle the strategy.

The online giant is just one of several American retailers – such as Wal-Mart and Toys R Us – to try its luck in the pre-owned market.