MP sales:

https://marketplace.tf/items/tf2/30919;5;u3001

Jan 9: 13.85 / 1.8 = 7.7 https://backpack.tf/item/7169620548

Jan 13: 13.85 / 1.77 =7.8

Jan 31: 13.99 / 1.76 = 7.9

Feb 9: 6.25$ at buy order price

Bot.tf sales:

https://bot.tf/stats/item?def=30919&q=5&ef=Showstopper&craft=1&aus=0&ks=0

1 @ 6 keys, 14.00 ref 15/01/2020

1 @ 6 keys 04/03/2020 https://backpack.tf/item/7454519000

1 @ 6 keys 28/03/2020

Other trades:

1. https://backpack.tf/item/6840623284

https://backpack.tf/profiles/76561198027363124#!/compare/1579824000/1584748800

Unusable

2. https://backpack.tf/item/6478484256

https://backpack.tf/profiles/76561198126139719#!/compare/1574812800/1580947200

Unusable

3. https://backpack.tf/item/6457593686

https://backpack.tf/profiles/76561198282751347#!/compare/1585440000/1585699200

Bought for 13 keys and 15 ref but with a Screaming Tiger Taunt: The Skating Scorcher. Even if outdated it would be a low outlier.

Taking 6 - 8 keys.