I think the biggest hangups people have are the "usable by" entry which blocks every thing, and a narrow level search. Most items jump by 2-3 levels with new gear. So for example (making up numbers) Chest armor exists at level 22 and 25, if you're level 24 and do a search for just 24 gear it looks like there is none. So like what was said above, make sure the level you use is a wide level range + or - 4 levels.
This! Usable By has never worked. Also, you usually need to choose a rarity, often times "standard" won't show you any items. And standard is crap anyway, so you aren't missing much.