When you buy used you are still buying a real copy of the game one that was bought at one point that helped the developer. If you buy from something like GS if they don't have enough copies they will need to buy more new ones. If you buy it from a person directly, then that is their money to do with as they see fit might help the game industry might not, but it is money they will spend again.
When you rent. Although you yourself are not paying the developer the copy you are playing is a legitimate one that had to be purchased giving money to the developer. If many people rent the game there will need to be more copies of the game in the store to meet the demand. More copies that will have been bought.
When you buy used or rent you are not putting a new copy of the game into the system of having a real one in your hands. So other people would need to get there hands on another real copy to buy or rent it themselves. When you pirate you just make it so it doesn't matter how many people want it vs how many their are since there can always be another copy making it so that no one needs to get more from the publisher if everyone is holding on to the copies they have.
If you buy a tv from someone unless they are giving up on tv they will probably get a new one. And since you bought the 1 tv they have no one else can buy it from them and will either have to find a used one elsewhere or buy a new one.
