Stop relying only on inspect screenshots and price tags. Use the game's own item resources—cases, collections, wear ranges, and StatTrak or Souvenir flags—to confirm what a skin actually is before you buy.
First, figure out where the skin comes from
A lot of people pick skins by staring at inspect screenshots and price tags, and rarely look back at the game's own resource library. In reality, every finish and every agent has a clear home in the client: it either hangs under a specific weapon case, sits in a collection list, or belongs to an operation or souvenir package. Nailing down this "family tree" is far more useful than refreshing inspect views over and over.
Open the Items page in your inventory and click any weapon case. You'll see the list of finishes it contains. That list is official, not compiled by a third party, so it carries version information by nature: which skins are standard drops, which are rare special items, and which have stopped dropping. The most common trap for buyers is conflating "collection" with "weapon case"—the former usually comes from map collections or operations, the latter is unboxed from cases, and their supply and wear distributions are completely different.
The case is a wear "birth certificate"
The most practical thing about a weapon case is that it writes the wear range into the resource. The same finish can have different wear ranges depending on the case: some run all the way from Factory New to Battle-Scarred, while others are capped between Minimal Wear and Field-Tested. When you're browsing listings on C5GAME, if a skin's wear bracket doesn't match the case resource, that's a red flag worth a second look.
On top of that, the case determines whether a StatTrak version exists. Only items marked StatTrak in the resource list have a counter; if it isn't marked, no amount of seller talk should convince you otherwise. This matters especially when picking knives and rifles, since the price gap between StatTrak and normal versions is often significant.
The collection page is an agent's ID card
Agents are a special case. Most agents come from specific collections or operation rewards, and opening the collection page in the client shows the full faction assignment and appearance grouping. Before buying an agent, confirm which collection it belongs to, then check whether that collection is still in production—that basically tells you how scarce it is.
One more detail: an agent's inspect animation and voice lines are bound in the resource, and different agents have different hand models, cuffs, and voice packs. When you look at images on C5GAME, it's best to cross-check with an actual in-game inspect, especially for glove and cuff occlusion—images and in-game angles often don't line up.
Treat resources as a reference table, not decoration
One last habit: every time you're about to buy an unfamiliar skin, spend two minutes in-game flipping through the corresponding weapon case or collection to confirm the finish name, wear range, whether it's StatTrak, and whether it's Souvenir. Once those four line up, then go check prices on C5GAME or the Steam Market and you'll feel grounded. The resource library won't tell you the price, but it will tell you what the item "should be"—the rest is the negotiation between you and the seller.