Proof below. Overpay calculated

Sales

http://www.tf2outpost.com/trade/14476480 - 17 keys

http://www.tf2outpost.com/trade/14246463 - Orb Fire Sola Topi, other guy added 2 keys = 16 keys

Side note: Took mid price since it was offered on

http://www.tf2outpost.com/trade/14444230 - NnB Shako + 4 keys (I think) = 16 keys

Side note: http://backpack.tf/id/76561198062734006?time=1379314800 <---> http://backpack.tf/id/76561198041563551?time=1379314800 - The 4 keys seem to match up

http://www.tf2outpost.com/trade/14401127 - 17 keys

http://www.tf2outpost.com/trade/14095015 - Steaming Juju for Noir + Steaming Tam, Noir = 18 keys

http://www.tf2outpost.com/trade/14072756 - Bubbling Noir + 1 key + Unknown Sweets = 16/17 keys (variable)

Notable Offers

http://www.tf2outpost.com/trade/14503405 - Offer of 19 keys

http://www.tf2outpost.com/trade/14503405 - Planets Robin = 17 keys

Conclusion

Several sales between 16 and 18 keys. I feel like 19 key offer is an outlier because of that, and I also saw several 18 key B/O's in closed trades.

Also: Never had a proper price suggestion :3

Help / Constructive Criticism / Additional Proof / Counter-Proof is ALWAYS welcome! >;3