Never go on any third party sites sent by a trader and never sign in there. People will get your APi key which can control your steam acount.
How to know if you are getting APi scammed?
You are sending items as gift to an account which looks exactly like the persons which you send your items to. but it has level 0 and its a brand new account.
To get out of this sticky situation:
You should
a) reset APi key
b) reset password
c) learn from your mistakes and dont go on 3rd party sites again.

Only trade with CS:GO items.
Even if you get an offer with a Dota 2 item which costs a lot of money. It is fake and you can look it up on market and see for yourself.
I am not an expert in arcs and tf2 items. So I dont deal with them.
Example is shown right here.
https://steamuserimages-a.akamaihd.net/ugc/998054113378568577/53EC6630BA42562491F6B9D041CC8D6F65C2B8C7/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

If you are getting a kato 2014 trade, you should always check the stickers first. To do that you have to
1. Go on this site (it is legit and many people use this site) csgo.exchange
2. Sign in
3. Go to Calculator > item float
https://steamuserimages-a.akamaihd.net/ugc/998054113378577853/094DBE5B9557F015DAF35FEAF29152993EE802DD/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false
4. Copy the inspect link of the item that has the stickers (just right click on inspect in game and click copy link adress)
https://steamuserimages-a.akamaihd.net/ugc/998054113378586223/B0C763E437B9F4A86339D938B7FD36BF26D08058/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false
5. Paste that link into the bar and in a few secs it should show you the wear of the stickers! In this case it has 0% wear
https://steamuserimages-a.akamaihd.net/ugc/998054113378593588/8E6E45380EBC85472BC2CA185020972D54241902/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

Never do cash in steam. Instant scam and you dont wanna get scammed. They can just get a skin off skin baron or any other site.
https://skinbaron.de/?language=en
Example of a good site to buy your skins from.

No you dont.
If the float of a pink / red is close to WW/Ft/MW IT DOESNT ADD ANY VALUE.
For example a low float redline .15 float doesnt add value.
Vulcan 0.36 float (close to ft) doesnt add value.
0.45 awp paw. doesnt add any value
Only close to factory new is getting a float add.
0.07 / 0.08 skins need a bit of overpay. Example.
https://steamuserimages-a.akamaihd.net/ugc/998054113378616113/541FBACE19323F2546D8E03F807BC17169AD7F73/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

• Never trade on cs money. Only buy skins there. Very profitable.
  
• Patience is a key to profit.
  
• Be smart.
  
• If someone wants your item. Overprice it by a bit.
  
• Your emotions control you. BE RATIONAL. Don't trade if you feel that something is wrong, you can always find another trader.
  
• NO ONE IS WILLING TO GIVE YOU MONEY. YOU CANT GET ♥♥♥♥♥♥♥♥♥♥.
  
• Don't trade with big traders. They always want overpay. And you will lose money.
  
• Don't trade skins which have an unstable market price. It might be good for you, but only if you're willing to take the risk to trade it.

https://www.youtube.com/channel/UCJ_GB1_bC_Mwkav57gCsFwQ?view_as=subscriber
The best way to support me is to sub to my YT. I try very hard to make good videos.
But other than that, you can find my trade link on profile.
Share this guide with other new traders so they don't get scammed.
Bye bye <3