Also, the prices for weapons on backpack.tf do change throughout the day as you can suggest prices on there. The reason for them selling a lower price than the original price is because of them making sure that the bots don't run out of ref/keys, weapons, etc... because that would basically make the bots useless and therefore scrap.tf would almost die out (unless jessecar/geel puts ref/keys and weapons in to the bots to continue the process, but that would take a lot of work).