The short answer is that once a game starts it’s “discount cycle” (i.e. -30%,-50% off etc.) people almost NEVER buy it a full price.  It’s just the way human beings are trained. 

Unless you’re a hard-core fan and you buy the game at launch (or within the first 3-4 months when it’s still full price) pretty much EVERYONE waits to buy the game when it discounted. After all, all games eventually go on sale at some point, and it’s just a matter of when.

So if you bought a game when it was on sale for say -50% and you un-check the box that says “Yes, sell this item if we find a buyer for you when it’s priced at a discount….etc.” there’s pretty much almost no possibility of your game being sold because the next person who wants the game is ONLY going buy it when it’s on sale, not at full price.

So some good advice, stop trying to game the system. If you purchased the game on sale, don't list it to sell ONLY at full price.  It’s most likely just never going to happen. It could, but you could also win the lottery.

So just remember, if you bought the game on sale, make sure the box is checked or it might just stay in your library.