First sign is that all of his +reps are around the same date by non experience traders, +rep groups on steam are still a thing
Second he's been on steam a year, Level does matter but a level 16 doing Paypal is 100% sketchy.
Third, he buys your items for paypal/Opskins currencty if you wan't to transfer it either make him go first and confirm it so he cant cancel the money being transferred.
Fourth, he has under 1.5k hours on csgo having around that amount will show that a trader has played the game enough to be experienced with the items, and dont be fooled by "I can send proof" anything can be easily photoshopped and you should know that best...
Fifth, NEVER go off of rep or how many trades they made you can trade to an alt account back and forth with a bot and easily get around 500 "Trades" in an hour
Lastly Im sorry to hear about that man, hope you can get your items back also if you're trading with someone talk to me I admittedly used to scam alot but I have stopped, but I now trade up my items and can try to help you with that I went from 25$ to 90$ withi and I know most tricks Good Luck trading man