Selling under 5 keys (if 1 key is 7.88 ref):

http://www.tf2outpost.com/trade/19876321 4.38 keys, 19 days, 4/4 in stock

http://www.tf2outpost.com/trade/19753264 4.51 keys, 7 days

http://www.tf2outpost.com/trade/19875755 4.51 keys, 29 days

http://www.tf2outpost.com/trade/19697717 4.63 keys, 27 days

http://www.tf2outpost.com/trade/19407213 4.72 keys, 26 days

http://www.tf2outpost.com/trade/19300332 4.89 keys, 31 days, 3/4 in stock

5 keys unsolds:

http://www.tf2outpost.com/trade/19812564 41 days

http://www.tf2outpost.com/trade/19878326 25 days

http://www.tf2outpost.com/trade/19581179 23 days

http://www.tf2outpost.com/trade/19861647 5 days

Sales at 5 keys:

http://www.tf2outpost.com/trade/19886789

http://www.tf2outpost.com/trade/19754186

I think he was just lucky... Looks like nobody want to buy this teddy bear. Since I couldn't find other sales, and they don't buy faster under 5 keys, I keep 5 keys in the range.