I'll add in screenshots and more errors as I go along.
almost always never happens, but you get an error, most of time it's errors listed below.
error: it just won't work. Just not your day.
error(8): you are not logged into steam, refresh the page and try again after logging in
error(16)/error(11)-courtesy of angry rock: the trade went through. refresh the page and the offer will no longer be valid
error(28): the trade is not working because of steam inventory issues. Try later.
error(you cannot trade with [so and so]): refresh the page, restart steam or http://steamcommunity.com/groups/tf2bazaar/announcements/detail/1477479091120204234
error(due to steam guard restrictions, you will be unable to trade from this device for 7 days): self explanatory