Remember that the spreadsheet lists the average price for the listed items. This means that some trades have the item cheaper, while others have it more expensive.

It also depends on how much the player values the item. I literally have less than one hour put into the Sniper throughout my whole TF2 career, as I do not find purely dexterity-based classes particularly interesting. This means that even a gold botkiller sniper rifle is worth nothing to me.

Also, since I like the Playground, I tend to offer discounts on trades to fellow members, like the one I replied to above.