If another user is bothering you over chat, or if see listings that are inappropriate or mislabeled, you can block that user. Blocking a user will mean you cannot see their listings, their store, or any chat messages.
There are three ways to block a user.
Block user from discovery
If you find an inappropriate or mislabeled listing in the discover view you can remove the listing by blocking a store from your view. Hover over the picture and you'll see the option to "block" appear on the bottom:
As soon as you block the user their listings will disappear from the discover view.
Block user from their page
You can also block a user directly from their page. If you're viewing the page, click on the button to the right of the "message" button:
Then click on the "block" button:
Block user from chat
To block a user from chat, click on the options button next to the X at the top of the chat window, then click "block."
If you need to unblock a user, go into Settings, click on the Blocked tab, and click "Unblock" on the right side of the screen.