Interesting things to note here is that there technically isn't direct proof that the 8 Key buyer resold for less, since the buyer has privated their inventory we can't confirm that it was directly sold to stn.

The "bulk" sale is not bulk at all. It sold alongside a Nuts & Bolts Soft Hard Hat for 16 Keys

https://backpack.tf/profiles/76561198311498888#!/compare/1748131200/1748217600

Looking at STN's current prices for both the Toy Soldier and Soft Hard Hat, it's very likely both were listed for 8 Keys, meaning this sale supports 8 Keys here. You should be cautious about mislabeling sales as bulk, however. If it's found that a sale classified as "bulk" is not actually a bulk sale, future suggestions will be closed due to cherry-picking.