The 4 key sellers are not succesfull, the supply is way bigger than the demand. Some people is even succesful buying them for 3 keys each.

Proof:

Unsold at 4 keys, i went through all 5 pages on tf2outpost.

http://www.tf2outpost.com/trade/14762070

http://www.tf2outpost.com/trade/14625960

http://www.tf2outpost.com/trade/14765726

http://www.tf2outpost.com/trade/14766815 "mid-end" bp.tf price.

http://www.tf2outpost.com/trade/14656343

http://www.tf2outpost.com/trade/14766737

http://www.tf2outpost.com/trade/14622122 offers, tho not a single offer of more than 3.5.

http://www.tf2outpost.com/trade/14330968

http://www.tf2outpost.com/trade/14766503 another "mid-end" bp.tf price

http://www.tf2outpost.com/trade/14609542

http://www.tf2outpost.com/trade/14584803

http://www.tf2outpost.com/trade/14595394

http://www.tf2outpost.com/trade/14723517

http://www.tf2outpost.com/trade/14449417

http://www.tf2outpost.com/trade/14737495

http://www.tf2outpost.com/trade/14765405

http://www.tf2outpost.com/trade/14664752

http://www.tf2outpost.com/trade/14761477

http://www.tf2outpost.com/trade/14763185

http://www.tf2outpost.com/trade/14728009

http://www.tf2outpost.com/trade/14689606

http://www.tf2outpost.com/trade/14671925

http://www.tf2outpost.com/trade/14760339

http://www.tf2outpost.com/trade/14723990

http://www.tf2outpost.com/trade/14754198

http://www.tf2outpost.com/trade/14720621

http://www.tf2outpost.com/trade/14755960 3.8 key seller.

http://www.tf2outpost.com/trade/14755701

http://www.tf2outpost.com/trade/14753958

http://www.tf2outpost.com/trade/14740460

http://www.tf2outpost.com/trade/14740324

http://www.tf2outpost.com/trade/14642617

http://www.tf2outpost.com/trade/14645764

http://www.tf2outpost.com/trade/14715354

http://www.tf2outpost.com/trade/14542048

http://www.tf2outpost.com/trade/14744963

http://www.tf2outpost.com/trade/14675862

http://www.tf2outpost.com/trade/14669552

Sellers and unsold for 3,5-ish.

http://www.tf2outpost.com/trade/14766966 3 key+2 ref seller.

http://www.tf2outpost.com/trade/14052116

http://www.tf2outpost.com/trade/14765376 3.5 key

http://www.tf2outpost.com/trade/14765136 3.5 key

http://www.tf2outpost.com/trade/14763755 3 key 3.66 ref.

http://www.tf2outpost.com/trade/14703730 3 key 5 ref

http://www.tf2outpost.com/trade/14761381 3 key 4 ref seller

http://www.tf2outpost.com/trade/14719859 unsold at 3,5

http://www.tf2outpost.com/trade/14677937 3 key 4 ref

http://www.tf2outpost.com/trade/14666774 some people added him, tho the trade is still up.

http://www.tf2outpost.com/trade/14742747

http://www.tf2outpost.com/trade/14744963

http://www.tf2outpost.com/trade/14741326

http://www.tf2outpost.com/trade/14713213 "3-4 keys"

http://www.tf2outpost.com/trade/14675307

Not a single 4 key buyer on outpost.

I seriously went through all 4 page of buyers on outpost, could not find a single 4 key buyer. Buyers:

http://www.tf2outpost.com/trade/14694021 3 key, succesful

http://www.tf2outpost.com/trade/14384470 3 key, succesful

http://www.tf2outpost.com/trade/14677926 3 key, no buyer yet.

http://www.tf2outpost.com/trade/14049206 bought one for 3 keys

http://www.tf2outpost.com/trade/14758774 3 key buyer, not succesful tho.

http://www.tf2outpost.com/trade/14451491 3 key buyer, someone offered one for 3 keys 5 ref

http://www.tf2outpost.com/trade/14689067 succesful 3 key buyer

http://www.tf2outpost.com/trade/14655015 3 key buyer, someone offerd one for 3.5

http://www.tf2outpost.com/trade/14542993 3 key buyer not succesful

http://www.tf2outpost.com/trade/14678719 3 key, someone said he sold one.

http://www.tf2outpost.com/trade/14728581 3 key one bought

http://www.tf2outpost.com/trade/14676512 3 key one bought

http://www.tf2outpost.com/trade/14407309 3 key buyer, someone offered one for 3.8 keys.

Classifieds @3,5 keys unsold for 3 days. http://backpack.tf/classifieds/search/id/521d757a4f96f4e60b8b4567

bonus trade: some guy who sold it for 1,5 keys, he obviously didn't knew what it was worth, but yeah. http://www.tf2outpost.com/trade/14745603