starter guide blurb version
Purchase Disabled Games (marked with "⎚" in your tradables or on the item page) are currently unavailable for purchase directly through the Steam store, therefore they may have vastly increased value on the grey key market (the only way they are available for purchase) in relation to their past value on Steam or ITAD. There are traders who may notice a new user's lack of experience and send an offer abusing that lack of experience. These traders use these new users' lack of awareness as to the value of their purchase disabled game to gain a significant profit. If a new user receives an offer which is [declined by mediator action] this is safe-guard against them accepting an abusive offer.
Have ⇄ : Want ★ ratio (h:w) is the number of different traders who have a game available to trade on Barter.vg, in ratio to the number of people that want it / have it wishlisted. Recent Humble Choice games may increase to 200-500 tradables.
The grey key market is an system of un-authorized game key sellers (not directly issued by game devs / Steam, instead resold by user, risky on the side of those re-sellers, as well as the grey key buyer) gg.deals tracks historical lows across un-authorized key sellers, however sellers use G2A for more profit.
IsThereAnyDeal (ITAD) can be used to check historical low sale prices for a game across all official key sources which that game is sold on. It also includes a price chart which can tell if a historical low is an anonmaly in that game's price history SteamDB tracks historical lows solely on the Steam Store
Humble Gift is preferred over keys for some traders because they can be checked if used, which keys can't, meaning that they can be stored with more assurances, before being re-sold on the grey market. Humble Bundle can tell if an abnormal amount of people have been accessed the gift link, and have deactivated accounts in the past and have a policy to do so in the future, taking all un-revealed keys with them.
Region Locked games are tagged with "region locked 🌐" you can go to a game's Barter page to see which bundle it applies to under the "Notice" area and clicking Humble Bundle, Fanatical, etc. icon to take you to the Barter bundle page, clicking on the 
"Steamgifts.com" button will lead you to information about the regions keys for the games for that bundle can be activated in or are excluded from.
curator connect / Dev - Game developers are abused by email spammers asking for game copies under the guise of review / giveaway / promotion
Curator Connect
"dev keys" are received by approaching as a youtube personality (with botted views / subs and template channels) and can be proven as being given away