[Proof below] This needs a update, nearly all trades at 2 keys are unsold and no offers.

Successful

http://www.tf2outpost.com/trade/9313865 (5.66 refs, claims to have bought 3)

http://www.tf2outpost.com/trade/9987390 (key +1 refs)

http://www.tf2outpost.com/trade/10089721 (key +0.66)

http://www.tf2outpost.com/trade/8650533 (1 key) <- 2 somewhat recent adds

http://www.tf2outpost.com/trade/9525008 (1.5 keys) <- has 4 in bp

http://www.tf2outpost.com/trade/10122585 (1.5 keys)

http://www.tf2outpost.com/trade/10058573 (5.11 refs, recent add)

Notable trades

http://www.tf2outpost.com/trade/9396924 (highest offer in a month being 1.75 keys)

http://www.tf2outpost.com/trade/10098451 (willing to sell for 1key 2 refs)

http://www.tf2outpost.com/trade/10160558 (1 key + 1.22 refs, 1 day)

http://www.tf2outpost.com/trade/9619615 (highest offer 1.5 keys, 3 weeks)

http://www.tf2outpost.com/trade/9855620 (highest offer 1.5 keys, 1 week)

http://www.tf2outpost.com/trade/8964667 (seller at 5.66 refs)

http://www.tf2outpost.com/trade/10138215 (selling at key +2refs)

Unsold <- most of not all with no offers (unless you wanna count 2 ref lowballers)

http://www.tf2outpost.com/trade/9842441 (1.5 keys, 2 weeks)

http://www.tf2outpost.com/trade/10056944 (1 key +3.66 refs, 5 days)

http://www.tf2outpost.com/trade/10169390 (1.5 keys)

http://www.tf2outpost.com/trade/10171458 (8 refs)

http://www.tf2outpost.com/trade/10146875 (2 keys, 1 day)

http://www.tf2outpost.com/trade/10165372 (2 keys, 1 day)

http://www.tf2outpost.com/trade/10156107 (2 keys, 1 day)

http://www.tf2outpost.com/trade/10151299 (2 keys, 1 day)

http://www.tf2outpost.com/trade/10177403 (2 keys, 1 day)

http://www.tf2outpost.com/trade/10161254 (2 keys, 1 day)

http://www.tf2outpost.com/trade/10154280 (key + 4 refs, 1 day)

http://www.tf2outpost.com/trade/10141700 (1 key, 3 refs, 2 days)

http://www.tf2outpost.com/trade/10086520 (4 refs, 2 days)

http://www.tf2outpost.com/trade/10133158 (2 keys, 2 days)

http://www.tf2outpost.com/trade/10142095 (2 keys, 2 days)

http://www.tf2outpost.com/trade/10134686 (2 keys, 2 days)

http://www.tf2outpost.com/trade/10124911 (2 keys, 2 days)

http://www.tf2outpost.com/trade/10140132 (2 keys, 2 days)

http://www.tf2outpost.com/trade/10131019 (2 keys, 2 days)

http://www.tf2outpost.com/trade/10119779 ( 2 keys, 3 days)

http://www.tf2outpost.com/trade/10118057 (2 keys, 3 days)

http://www.tf2outpost.com/trade/10116147 (2 keys, 3 days)

http://www.tf2outpost.com/trade/10120701 (2 keys, 3 days)

http://www.tf2outpost.com/trade/10124314 (2 keys, 3 days)

http://www.tf2outpost.com/trade/10123897 (2 keys, 3 days)

http://www.tf2outpost.com/trade/10095791 (2 keys, 3 days)

http://www.tf2outpost.com/trade/10093589 (1 key +3refs, 4 days)

http://www.tf2outpost.com/trade/10103535 (2 keys, 4 days)

http://www.tf2outpost.com/trade/10090955 (2 keys, 4 days)

http://www.tf2outpost.com/trade/10112331 (2 keys, 4 days)

http://www.tf2outpost.com/trade/10098535 (2 keys, 4 days) <- lvl 100

http://www.tf2outpost.com/trade/10096446 (2 keys, 4 days)

http://www.tf2outpost.com/trade/10092256 (2 keys, 4 days)

http://www.tf2outpost.com/trade/10094581 (2 keys, 4 days)

http://www.tf2outpost.com/trade/10120343 (2 keys, 4 days)

http://www.tf2outpost.com/trade/10088680 (2 keys, 4 days)

http://www.tf2outpost.com/trade/10027136 (2 keys, 6 days)

http://www.tf2outpost.com/trade/10068829 (2 keys, 5 days)

http://www.tf2outpost.com/trade/9862449 (2 keys 5 days)

http://www.tf2outpost.com/trade/10074061 (2 keys, 5 days)

http://www.tf2outpost.com/trade/10056379 (2 keys, 5 days)

http://www.tf2outpost.com/trade/10046207 (2 keys, 6 days)

http://www.tf2outpost.com/trade/10032063 (2 keys, 6 days)

http://www.tf2outpost.com/trade/9921657 (2 keys, 1 week)

http://www.tf2outpost.com/trade/9870916 (2 keys, 1 week)

http://www.tf2outpost.com/trade/9875723 (2 keys, 1 week)

http://www.tf2outpost.com/trade/9961066 (2 keys, 1 week)

http://www.tf2outpost.com/trade/9883889 (2 keys, 1 week)

http://www.tf2outpost.com/trade/9935353 (2 keys 1 week)

http://www.tf2outpost.com/trade/9712312 (2 keys, 2 weeks)

http://www.tf2outpost.com/trade/9808356 (2 keys, 2 weeks)

http://www.tf2outpost.com/trade/9756927 (2 keys, 2 weeks)

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-3 trades unsold at 1.5, 1.77, 1.88 keys.

-9 trades unsold at 2 keys

Hopefully i didnt repeat any links by accident...Pretty clear that 2 keys is out of the question, some are sold to quick buyers for around 1 key (not enough are sold at that price fir it to drop). 1.5keys seems to be accurate based on the offers and unsolds.

Can Probably go even lower but for how this is the best proof i can show xD

feel free to post counter proof if im wrong :)