I've seen this go so many damn times for 3 keys on trade.tf, I am inspired to make this suggestion. Well, lets move on since I cant make an "Original" joke >.> (bad pun is bad)

Sellers (keys)

http://backpack.tf/classifieds/search/513/11/0 - 6 at 3 keys, 1 at 3.1, 2 at 3.2, 1 at 3.17, 7 at 3.3 and the list goes on...

3

http://www.tf2outpost.com/trade/13136914

http://www.tf2outpost.com/trade/13135803

http://www.tf2outpost.com/trade/13128721

http://www.tf2outpost.com/trade/13104898

http://www.tf2outpost.com/trade/13102341

http://www.tf2outpost.com/trade/13094736

Unsolds above 3 keys

http://www.tf2outpost.com/trade/13110913 - 3.35, 21 hours

http://www.tf2outpost.com/trade/13019739 - Bp.tf prices, 3 days

http://www.tf2outpost.com/trade/13069380 - 3.55, 2 days (3.35 = 3 keys + 3 ref, 3.5 keys = 3 keys + 2.82 ref, so, due to the little difference, Ill include 3.55)

http://www.tf2outpost.com/trade/12448402 - 3.2, 2 weeks (Heehee, I will go against your will, my friend! >;3)

http://www.tf2outpost.com/trade/13057528 - 3.2 keys, 2 days

http://www.tf2outpost.com/trade/13074460 - 3.4, 2 days

http://www.tf2outpost.com/trade/12872890 - 3.55, 1 week

http://www.tf2outpost.com/trade/12766790 - 3.55, 1 week

http://www.tf2outpost.com/trade/13107093 - 3.35, 1 day

http://www.tf2outpost.com/trade/13133715 - 3.2, 3 hours

http://www.tf2outpost.com/trade/13122015 - 3.5, 12 hours

http://www.tf2outpost.com/trade/13133448 - 3.35, 2 hours

http://www.tf2outpost.com/trade/13046055 - 3.2, 3 days

http://www.tf2outpost.com/trade/13101795 - 3.5, 1 day

http://www.tf2outpost.com/trade/13107419 - 3.2, 23 hours

http://www.tf2outpost.com/trade/12874517 - 3.5, 1 week

http://www.tf2outpost.com/trade/13049881 - 3.5, 2 days

http://www.tf2outpost.com/trade/13101124 - 3.5, 1 day

http://www.tf2outpost.com/trade/13090601 - 3.45, 1 day (x3)

http://www.tf2outpost.com/trade/13064160 - 3.3, 2 days

http://www.tf2outpost.com/trade/13113796 - 3.2, 19 hours

http://www.tf2outpost.com/trade/13071285 - 3.55, 2 days

http://www.tf2outpost.com/trade/13028514 - 3.2, 2 days

http://www.tf2outpost.com/trade/13100371 - 3.2, 1 day

http://www.tf2outpost.com/trade/13109939 - 3.4, 21 hours

http://www.tf2outpost.com/trade/13038313 - 3.5, 3 days

http://www.tf2outpost.com/trade/13132172 - 3.2, 5 hours

http://www.tf2outpost.com/trade/13096571 - 3.55, 1 day

http://www.tf2outpost.com/trade/13124980 - 3.55, 10 hours

http://www.tf2outpost.com/trade/13051064 - 3.35, 2 days

Sold

3

http://www.tf2outpost.com/trade/13091574

http://www.tf2outpost.com/trade/13087507

http://www.tf2outpost.com/trade/13136639

http://imgur.com/qdCLDkd

http://www.tf2outpost.com/trade/13130251

http://www.tf2outpost.com/trade/13126757

http://www.tf2outpost.com/trade/13126130

http://www.tf2outpost.com/trade/13110722 (strange part)

http://www.tf2outpost.com/trade/13109553 (strange part)

http://www.tf2outpost.com/trade/13102271

http://www.tf2outpost.com/trade/13101331

http://www.tf2outpost.com/trade/13099836

http://www.tf2outpost.com/trade/13099710

http://www.tf2outpost.com/trade/13097806

http://trade.tf/listings/search/Sell/Strange/Original/all/19 - Proof it was 3 keys ^

http://www.tf2outpost.com/trade/13094762

http://www.tf2outpost.com/trade/13094101

http://www.tf2outpost.com/trade/13092058

http://trade.tf/listings/search/Sell/Strange/Original/all/24 - Proof that above was 3 keys

http://www.tf2outpost.com/trade/13086150 (read the comments)

http://www.tf2outpost.com/trade/13080822

http://www.tf2outpost.com/trade/13078253

Other

http://www.tf2outpost.com/trade/13121828 - Accepted offer of 2 keys + 2 ref + Pink Paint = 3.1-ish - http://www.tf2outpost.com/trade/13121828 - SharkTopus got it for 2 keys + 1 pink paint (2.7 keys) here instead

http://www.tf2outpost.com/trade/13113682 - 3.15

http://www.tf2outpost.com/trade/13107799 - 3.5

http://www.tf2outpost.com/trade/13103707 - 2.45 keys

http://www.tf2outpost.com/trade/13091471 - 3.2

Conclusion

So many selling and sold at 3 keys, not enough for less or more to give it a range. I would've listed more, but I really had to go >.< Vote accordingly

Help / Consturctive Criticisim / Additional Proof / Counter-Proof is ALWAYS welcome! :D

EDIT: I just realised I forgot unsolds, damn. Well, I can't add them now. I've got school tomorrow, and its night here. Will be a while before I can show more proof. If some one actually helps me find some, that would be GREATLY appreciated ^.^

EDIT (v2): Well, I added some unsolds. I know its not a lot and some of it is even < 1 day old :/ Hope this helps a bit though. (Yay for my sister's laptop! ^.^)