Auto-accepting trade offers by following rules:
* Steam trading cards only (common or foil, not emoticons nor backgrounds)
* The same number of cards from the same games sets (1:1 / 3:3 / 7:7 etc)
* No trade hold (Steam App/2FA Authenticator on)
As my type is Fair in ASF-STM terms, your trade offer must be either good or neutral for me:
* Good: A A -> A B // A A _ C D E <> _ B B C D E
* Neutral: A B -> A C // A B _ D D E <> A _ C C D E
i.e. do not break my set completion (Bad: A C -> A A // A B C _ E E <> A A B _ D E = offer ignored).

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If your offer was not accepted (almost) instantly, then it is not valid to rules above and was ignored. So you have to cancel it and check my set completion state right before sending an offer.

In some cases (e.g. I have only 4 different cards without duplicates out of 5 in set // A B C _ E) it might been manually accepted later (up to a week, because of real life things, like touching grass).

Instantly declined trade offers means trade blocklisting for suspicious abusive behaviour (1$:1c, trades just for marketable pricier cards without intention to complete the set).

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Feel free to add me for easier finding needed cards via game badge pages.
I recommend to use ASF-STM script as it will find you possible matches with me and other users.

List of useful tools:
https://asf.justarchi.net/STM and free matching script for it: https://github.com/Rudokhvist/ASF-STM or https://github.com/iBreakEverything/ASF-STM-Enhancement
https://github.com/Mr-VIT/SteamWebTools
https://github.com/SteamDatabase/BrowserExtension
https://github.com/IsThereAnyDeal/AugmentedSteam