Ok, so you sit down with a person to play this in real life. The rules are fully explained to both players. First you have to figure out, does this opponent understand game theory, and will only trade a 1, or are they going to play sub-optimally?
You’ve decided that you believe your opponent will play sub-optimally and they are willing to trade a non-1. What do you think they will trade? Someone of reasonable intelligence who doesn’t put too much thought into the game will probably trade a 1, 2, or 3, probably not a 4, 5, or 6. In that case if they are willing to trade, you can assume their card is 1, 2, or 3. Of course, if you are willing to trade, that means you also have 1, 2, or 3.
If you have 3, you’re not willing to trade with someone also willing to trade, since they can’t have the 3, you have it. You’re basically guaranteed to be losing that one.
If you have a 2, you’re going for a 50/50 that they have a 3. There is a bit more weight on the chance of them having a 1, though, in case you were wrong about their ability to understand game theory.
If you have a 1, you would have traded anyway no matter if the other person understands the game theory or not.
If you believe your opponent is foolish, the only major change in strategy is that you might be willing to trade a 2 a little less than half the time. The other trades you are willing to make, your opponent is not willing.