https://backpack.tf/item/7304549015 - looks like buyer sold to stn.tf ~1 week later (assuming this is the history, possible it could be a hidden one though)

https://stntrading.eu/item/tf2/Unusual+Poisonous+Bubbles+of+Regret+Taunt%3A+Most+Wanted - likely for ~3 keys 20 ref

https://backpack.tf/profiles/76561198311498888#!/compare/1593648000/1593734400

https://backpack.tf/profiles/76561199008475806#!/compare/1591660800/1594339200

Stn's selling; Doesn't look like a sale. Could be to a private inv, which if it was, they probably bought for ~5 keys (see stn ss above) and then eventually got to Gergie in that massive bulk seen in the 2nd compare.

New sale:

https://marketplace.tf/items/tf2/30614;5;u3019

$10.83 / $1.93 = 5.61 keys

No B/O or history found

I would go 5.5 flat here off the new sale, considering the circumstances around the first sale.