Sale 1:

https://backpack.tf/profiles/76561198317606171#!/compare/1545004800/1545177600

(other side is unclear)

Unclear

Sale 2-3:

https://marketplace.tf/items/158;5;u61/

= $27 / $1.8 (Mar 9)

= 15 keys

= $26.29 / $1.8 (Feb 10th)

= 14.60...

~ 15 keys

Sale 4: ~ provided by K1ng, thank you again for finding this sale.

https://backpack.tf/profiles/76561198317606171#!/compare/1550102400/1550188800

https://bot.tf/stats/listings/M1NQDGOY ----- Listed since (at least) Jan 17th

= 11 keys

Summary: 11, 15, 15

Seller: 12 (2 months old)

Conclusion: pricing at 11 keys, the 11 key sale took at least 1 month to sell. Hence, the exclusion of the sales at 15 keys.