I might be wrong in my detective work again here, but it's looks like Tornkriptonix -> chraule in this history had another user inbetween who bought/sold quickly.

Looks to me like Tornkriptonix traded the baker boy with hotsalt for a gifted bubbling rack

Then hotsalt traded the baker boy with chraule for a disco beat down helmet without a home

http://www.tf2outpost.com/trade/26712330 - confirms hotsalt -> chraule

Baker boy history: http://backpack.tf/item/3153469100

Rack history: http://backpack.tf/item/1365011547

Helmet without a home history: http://backpack.tf/item/2286786765

Mini for gifted bubbling rack - sold for 20 keys

http://backpack.tf/profiles/76561198043768687?time=1437980400 (July 27th)

http://backpack.tf/profiles/76561198043768687?time=1438066800 (July 28th)

http://backpack.tf/profiles/76561198043768687?time=1438066800&compare=1437980400

So that's 2 sales ~18-20 keys.

18-22 might be better for now, though the rack sale seems to have occured without advertisement and the hwah sale occured quickly, so idk... could be called quicksales and support this range too. Maybe see what others think.

Also, as I told you before, you shouldn't apply overpay in your mini and your sale. Only do overpay once for each sale that occurs (basically just don't do overpay in minis.)