Smoking Field Practice sales:

Marketplace in-date sales - https://marketplace.tf/items/tf2/30862;5;u35

Avg. price of keys - https://marketplace.tf/items/tf2/5021;6

1. Mar. 29th - 24.99 (24.99/1.69=14.78) 15 keys

2. Apr. 1st - 31.51 (31.51/1.69=18.64) 18.5 keys

3. Apr. 27th - 31.51 (31.51/1.82=17.31) 17.5 keys

Sale #1 - Untraceable: Unable to find a sale price here

https://backpack.tf/profiles/76561198118925864#!/compare/1581552000/1583366400

https://backpack.tf/profiles/76561198337734785#!/compare/1583193600/1583280000

Item History: https://backpack.tf/item/7965909105

Sale #2 - QS: 10 keys pure

https://backpack.tf/profiles/76561198135388328#!/compare/1581465600/1581552000

https://backpack.tf/profiles/76561198125184142#!/compare/1581552000/1581638400

Item History: https://backpack.tf/item/6178417276

Going to go with the range of sales on marketplace; 15-18.5 keys