Hi so i realized that there have been most keys priced at 7.88 and i have hardly seen any priced at 8 ref as it is valued at on backpack.tf, for example the backpack.tf page for the key shows that many sell their keys for 7.88 however rarely now some people sell them for 8 ref which is why i have specified that the key's high price should be 8 refined here is the key's page :

http://backpack.tf/stats/Unique/Mann%20Co.%20Supply%20Crate%20Key/Tradable/Craftable

some proof http://www.tf2outpost.com/trade/21708017