Hello Don.
You might think this is scamming, but it's really not. What they did was just a dick move and you should always take a second look before accepting a trade, make sure you're more careful next time.
SSRP Rules wrote:
How to avoid being scammed
- If a trade or deal seems good to be true, it’s most likely a scam.
- If the other player is requiring you to give them valuable items saying they will give you other items back in another trade, it is likely a scam.
- For very rare or expensive items that you’re not willing to lose. Do not drop them or gamble them at any point.
- Keep your account information secure. Only ever enter your ZARP account details on www.zarpgaming.com And remember a ZARP staff member will never ask for your password.
- ALWAYS check the trade menu carefully before pressing the Confirm trade button.
- Never give out more that you are willing to lose.