You're still expected to validify the person you're trading has the stand you want before trading them. Which is done using the !check command (which I assume you know.) If you only "saw" it, it is your fault for not using the check command which would show you what they had.
Also, did you ask the person to trade before sending the trade? Or did you just send the trade without saying anything to them? If it's the second it's your fault because they could have changed stands because they wanted to use a different stand but then you sent it and they accepted it thinking you were sending a trade for that stand.