The original Idle Master was released almost 6 months ago and to my knowledge nobody has gotten in trouble for using it. Once you've obtained those cards, you can't continue receiving more. When you purchase a game that has trading cards you're entitled to a certain number of cards. It's also worth noting that unlike the TF2 idling servers, this program isn't giving you anything you're not already entitled to receive. This is most likely why programs like this haven't been addressed in any updates to the Steam Subscriber Agreement. In this sense, Valve and the developers make more money the more cards you sell. The money you're 'earning' is coming from other users purchasing your items from their wallet balance. The game developers get 5% of that transaction as well.
Valve shouldn't take any issue with you idling and selling the cards on the community market, because they get a 10% cut for each item sold.
