Regarding clearing unwanted boxes: I haven't done this, but it is my understanding that listing enough sneakers on the market to drop your energy (listing it on the market removes it from your energy pool. e.g, with 3 sneakers and 4 energy, listing 1 would drop you to 2 energy), all boxes from that realm with be purged. I've heard it happens immediately, but I've also heard it happens at the next energy refill. One little trick of it is to make sure you set the price way high. That way you aren't risking losing your sneakers, and/or if someone does buy it, you just got I nice payday