Sale 1-4:

https://marketplace.tf/items/tf2/30332;5;u62

$33.33 / $1.79 = 18.62 keys // https://backpack.tf/item/7955657790

$32 / $1.79 = 17.88 keys

$30 / $1.80 = 16.67 keys

$26.2 / $1.77 = 14.80 keys // https://backpack.tf/item/7956710417

Sale 5:

untrace, possibly MP sale 3

https://backpack.tf/profiles/76561198066059505#!/compare/1573516800/1573689600

https://backpack.tf/profiles/76561198241622178#!/compare/1573603200/1573689600

Sale 6:

untrace

https://backpack.tf/profiles/76561198363395191#!/compare/1572912000/1572998400

https://backpack.tf/profiles/76561198061707281#!/compare/1572912000/1573171200

Sale 7:

13 pure

https://backpack.tf/profiles/76561198928347702#!/compare/1570492800/1570579200

https://backpack.tf/profiles/76561198079346028#!/compare/1570406400/1570579200

Sale 8:

untrace

https://backpack.tf/profiles/76561198101623903#!/compare/1571961600/1573603200

https://backpack.tf/profiles/76561198363395191#!/compare/1573516800/1573603200

Sale 9:

untrace

https://backpack.tf/profiles/76561198363395191#!/compare/1573603200/1573689600

https://backpack.tf/profiles/76561198380648009#!/compare/1573603200/1573689600

Sale 10:

bulk / gamble

https://backpack.tf/profiles/76561198063075911#!/compare/1573689600/1573776000

https://backpack.tf/profiles/76561198380648009#!/compare/1573689600/1573776000

Sale 11:

untrace

https://backpack.tf/profiles/76561198063075911#!/compare/1573776000/1573862400

https://backpack.tf/profiles/76561198082824979#!/compare/1573776000/1573948800

Sale 12:

18 pure

https://backpack.tf/profiles/76561198190155685#!/compare/1575849600/1576022400

https://backpack.tf/profiles/76561198175470618#!/compare/1575936000/1576022400

Sale 13:

using there

CPS tossle

https://backpack.tf/profiles/76561198175470618#!/compare/1576108800/1576195200

https://backpack.tf/profiles/76561198107793922#!/compare/1576108800/1576195200

Sale 14:

untrace

https://backpack.tf/profiles/76561198107793922#!/compare/1576886400/1576972800

https://backpack.tf/profiles/76561198207603105#!/compare/1576713600/1576886400

Sale 15:

use there

steaming cotton head + 5 keys

https://backpack.tf/profiles/76561198803791472#!/compare/1577145600/1577232000

https://backpack.tf/profiles/76561198207603105#!/compare/1576972800/1577232000

Sale 16:

untrace, probs 17 tho

https://backpack.tf/profiles/76561198803791472#!/compare/1577232000/1577404800

https://backpack.tf/profiles/76561198067332644#!/compare/1577318400/1577404800

Sale 17:

PE Vanquisher(31)

https://backpack.tf/profiles/76561198067332644#!/compare/1577404800/1577491200

https://backpack.tf/profiles/76561198402368483#!/compare/1576972800/1577491200

==============================================================================

Sales:

13,15,17,18,18,19,31

buyers at 13: https://imgur.com/a/oL32hPI

excluding 31 as high outlier