https://forums.backpack.tf/topic/6033-rules-for-unusual-price-suggestions/

Using screenshots of bot.tf(Gladiator) sales as proof: We now allow screenshots of bot.tf(Gladiator) stats pages as proof if there are 3 sales at that value. We didn't allow them in the past because an item could have also been sold for items and not the pure buyout. With that being said, a majority of bot.tf sales still happen at their pure buyout so if there are 3 sales for a certain value, chances are incredibly high that at least 1 of them was for the pure buyout, or overpay in items that would be capped at the buyout. You can access that page here if you donated at least 1 key to bot.tf.