Item 1:

https://backpack.tf/item/15789493376

Sale 1:

https://backpack.tf/profiles/76561198019868868#!/compare/1769212800/1769385600

https://backpack.tf/profiles/76561199564942025#!/compare/1769212800/1769299200

no idea

Sale 2:

https://backpack.tf/profiles/76561198402163029#!/compare/1772064000/1772150400

https://backpack.tf/profiles/76561198019868868#!/compare/1769385600/1769558400

no idea

Sale 3:

https://backpack.tf/profiles/76561198402163029#!/compare/1769472000/1769558400

https://backpack.tf/profiles/76561198019868868#!/compare/1769385600/1769558400

8 keys + 15 refs apparently

Sale 4:

https://backpack.tf/profiles/76561198402163029#!/compare/1769644800/1769731200

https://backpack.tf/profiles/76561198346781793#!/compare/1769644800/1769731200

8 keys + 1.77 refs

Sale 5:

https://backpack.tf/profiles/76561198346781793#!/compare/1769731200/1769817600

https://backpack.tf/profiles/76561198061836787#!/compare/1769731200/1769817600

9 keys

Item 2:

https://backpack.tf/item/15924346411

Sale 6:

https://backpack.tf/profiles/76561198175456289#!/compare/1770249600/1770336000

https://backpack.tf/profiles/76561198850121720#!/compare/1770249600/1770336000

dumped for something idk

Item 3:

https://backpack.tf/item/7970047091

Sale 7:

https://backpack.tf/profiles/76561198854496201#!/compare/1766188800/1766275200

https://backpack.tf/profiles/76561199020164416#!/compare/1766275200/1766361600

dunno

Sale 8:

https://backpack.tf/profiles/76561199020164416#!/compare/1768089600/1768262400

https://backpack.tf/profiles/76561199235746160#!/compare/1768176000/1768262400

dunno, histories are fucked

Sale 9:

https://backpack.tf/profiles/76561198113084770#!/compare/1768003200/1768262400

https://backpack.tf/profiles/76561199235746160#!/compare/1768262400/1768348800

trade between bot and its owner i g

Sale 10:

https://backpack.tf/profiles/76561198113084770#!/compare/1768262400/1768435200

https://backpack.tf/profiles/76561199183171982#!/compare/1768262400/1768348800

based on seller's side its 8 keys + 2.11 refs

Sale 11:

https://marketplace.tf/items/tf2/31041;5;u12

https://marketplace.tf/items/tf2/5021;6

15.99$ on 11th of February (I think this sale is the one in item 3's history)

15.99/1.87=~8.5 keys

Item 4:

https://backpack.tf/item/8000761201

Sale 12:

https://marketplace.tf/items/tf2/31041;5;u12

https://marketplace.tf/items/tf2/5021;6

15.99$ on 14th of March

15.99/1.9=~8.5 keys

Item 5:

<history unknown>

Sale 13:

https://marketplace.tf/items/tf2/31041;5;u12

https://marketplace.tf/items/tf2/5021;6

15$ on 21st of December

15/1.83=~8 keys

Sales ranging from 8 keys up to 9, so going with that as a range.