The way I do it is I go on [ Register or Signin to view external links. ] They constantly Update the prices for skins and knives they might not have it correct all the time but it gives you a good idea on how much it costs. From there I also look at the same skin amounts( So lets say 5 elite builds as an example) and I look at how much those elite builds are going for. When I want to make a trade I go on [ Register or Signin to view external links. ] it is a trusted website but beware of scammers check here Forums/t=7063741/trading-scams-an...dated.html
(credit to Prohibit)
You can easily search up the item you're looking for and what you're willing to give for that item
Example: You want an M4-S Guardian in return you're willing to give 5 keys You can submit those offers.

When people are trading for "pure" also known as keys, then items are worth about 80% - 90% of their value, depending on who is trading. So with 35 keys, which cost $87.50, you might be able to get right around $100 knife. Again, depending on who you trade with. Trading is tough, there are YouTube videos that can give you tips and what not, but I'd say trial and error is the best way to go. Trading also takes a long, long time. You wont find 1 person and then trade for whatever you want, they are going to try and lowball you or make you overpay, so be careful. Good luck!

TY, What skins should i trade with?

I heard asiimovs are good for trading as well as redlines maybe you can try a cyrex since you're trading with keys People on csgo lounge are always making trades for keys just observe and when you think you found a right deal go for it.