Insta-Sell is an option that some websites offer to buy your skins instantly, because of the new trade hold update some sites can still hold the balance for up to 8 days though.
% was calculated using the average price of 4 skins – Galil Eco FT, AK Redline FT, AWP Asiimov FT and Butterfly Crimson Web FT and compared between the Insta-Sell prices and cheapest prices of same skins on Buff.