Additionally, the Commercial usage guidelines state that you may sell cosmetic items, except for “capes”, if the item sold does not give a user an unfair gameplay advantage over anyone else on the server. Due to this, you are not allowed to sell the following for hard currency:

The ability to:
use a portable crafting table, chest, ender chest, compass, etc.
set the time of day or weather, for yourself or others, other than in places where the intended server's gameplay does not occur, such as the lobby of a minigame server.
clear your inventory.
respawn.
create teleportation points, no matter who can use them (commonly referred to as “warps”).
teleport to a saved location (commonly, the /home command).
teleport to your last location (commonly, the /back command).
see other players’ inventory, other than in creative mode.
see a list of players that are nearby, other than in creative mode.
see the crafting recipe for an item, or the ability to craft an item automatically.
remove the enchantment from an item.
automatically sell blocks that you mine.
automatically compress resources to their block form.
fly in places where the intended server's gameplay occurs.
edit several blocks at the same time, regardless of where on the server you can do it.
keep your inventory or specific items when you die.
A non-cosmetic item or perk:
that is dropped in an area accessible by everyone, whether other players are notified of the drop or not.
as a prize after fighting a boss in an area accessible by everyone, whether other players are notified of the event or not.
Bedrock blocks or other non-cosmetic items.
Schematics, regardless of the game mode.
Higher bandwidth, or other improved connections to the server.
Access to contests based on stats (i.e. most blocks mined etc.), if the prize is not cosmetic.
Decreased cooldown for non-cosmetic commands.
Items or perks that affect gameplay or give the player an unfair advantage, even if they are also available through soft currency purchase, or just by playing the game for a certain time.