It shows how bad at economic these companies are. It all depends on the total cost. The cost to play a game is what you pay minus what you can sell it for. If a game coss $70 new but you can sell it for $40 in a month the cost to you is $30. That is what you are willing to pay. If they kill the second hand market then the real cost will be $70. You will now sell a lot fewer games because if the higher price. If they kill the second hand market but drop the price to $30 they will sell about the same as before. Now the trick is to figure out which gives you the highest total revenue. I don't think DRM is going to help.
That would be true if we humans were rational. You make sense but that is why you may be wrong. Its up to them to pull off the trick. Lets hope they go out of business.
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