Before you sell Team Fortress 2 items you’ve garnered, it’s good to know what makes a difference in terms of market prices. From the types of items mentioned above, Weapons, Cosmetics and Taunts have certain additional attributes that most of the time influence their value.
Item quality is bound both with item’s rarity and specific modificators, although not in all cases. Normal items are just that, standard loadout with grey names. Unique items with yellow names are less common, and may bring some variation to standard loadout, yet it’s still the basic item quality for drops, achievement prizes and basic crafting results. Blue Vintage items are Unique items crafted before Mann-Conomy Update, therefore with a slightly higher collectible value, although it’s not a stable relation. Genuine items with green names are gained via cross-game promotions or special in-game events, and are thus colored differently to discriminate them from usually dropped unique and normal items. They also retain their color if they are strangified. What does that mean? Strange items are similar to StatTrak items from CS:GO, but there are several main differences. You can not only drop strange items, but you can also use a strangifier to make them strange. Once a weapon is strange, it keeps track of kills scored with its use. This, in comparison to CS StatTrak, causes them to gain new prefixes with consecutive tiers reached by the number of kills. Also, non-weapon items can also be strange tracking other events instead, like Jarate tracking the amount of coated victims or Invis Watch tracking the number of seconds you remain invisible. The most noteworthy items in the bunch are purple Unusual items, which give weapons and cosmetic items additional particle effects. They are a rare loot from crates and are hard to obtain otherwise, making them the rarest and usually most sought for items in TF2. There are also teal Haunted items which can be looted during yearly Halloween events, but their quality and rarity are similar to those of Normal and Unique items.
A quality grade we have to discuss separately is the Decorated quality. This is for weapons that have a cosmetic skin applied. In Team Fortress 2 the skins are identified universally and then applied to certain weapons. Decorations have their rarity grades and wear levels. From the most common to the rarest the grades are Civilian, Freelance, Mercenary, Commando, Assassin, and Elite. Civilian Grade finishes are those found more often and Elite Grade finishes are the most uncommon ones. The wear level, in turn, should sound familiar to CSGO players, because they are basically the same. From high float to low they are, Battle-Scared, Well-Worn, Field-Tested, Minimal Wear, Factory New. In most cases the lower the float of a weapon skin, the more valuable a skin is, but you will find exceptions to that rule.
There are also other item qualities, like the ones denoting an item being tested from the Community Workshop, but they don’t have a market referential value, so we’ll describe them in a quality-dedicated post in the future.
Item levels are an aesthetic remnant of the early development of additional item properties and, although at first they were meant to make way for some game-influencing mechanic, they ended up being just another numeric property. As such, they have no influence of value while selling TF2 items for money. However, per collector’s value, some levels will be more desired and also favorably valued while trading. When looking for leveled Team Fortress 2 items to sell, take notice of those with levels like 1, 42 or - who could have guessed - 69, as those are usually called out for more.
If you want to evaluate items other than weapons and cosmetic ones, or if your math simply fails you, there are websites like backpack.tf that will help you determine the value of your equipment for you.