high level/power heroes on very low level quest should not break their items since these heroes can do the quest without any equipment. Now if you want to get some low level material you have to unequip some heroes for saving your items
The market is so difficult to use. The only reason I can think of is that the developors intend to do so. They make us very difficult to find the item we want to replace the broken ones. Every time you struggle to find an item, you lose some of your willpower and eventually can't stand it and use gems to repair. It is very easy in programming to sort by anything you want.
 "Shop Heroes"){kind=icon}
Thanks for the feedback, Tracyiwen. We may add more sorting features to the Trade House in the future.