I typed all of this out to explain to someone, and figured it might be a nice idea to share with the general public.
There are several different grades of skins (in order of rarity) White (Common) - Consumer grade Light blue (Uncommon) - Industrial grade Darker blue (Rare) - Mil-spec Purple (Mythical) - Restricted Pinkish purple (Legendary) - Classified Red (Ancient) - Covert
After matches, there is a chance to drop either a crate or a skin
A skin that drops after a match will be of a random map collection, and the tier will be White through Purple. (only exceptions are SCAR-20 | Splash Jam of the Militia collection and P250 | Franklin of the Bank collection, which are are Pink-tier)
If you unbox a crate, the tier will be Darker Blue (mil-spec) through Red (covert).
Generally, the more rare an item is, the more it will be worth. However there are exceptions, like if a skin is more used. This is why M4, AK, AWP, and Glock skins generally are more expensive than other skins on the market.
Canals is a brand new map for CS:GO, set in a historic Italian city. Two important tourist attractions is under threat by an international group of terrorists known as the Phoenix, and SEAL Team 6 has been deployed to stop them.
The map is based on the real-world environments that give each area its own architectural style as well as gameplay, and produce an unconventional layout. The CT side is composed of a large, wide open area while T-controlled territory forms a crescent of smaller spaces around it and provides multiple approaches to each bomb site.