In Search Of. Many folks use it if they are specifically looking for something; an example I'm ISO Molasses, I'd go make a Marketplace Trade, specifically seeking out Molasses and I would tell people to send me a Private Trade ((Not on my ISO post)), offering up Molasses and I'd go from there, until I no longer needed Molasses and then, I'd delete the post.

Oh ok how do you make one?

when making the trade, click the “Searching For” button, if it turns yellow then you've set the trade to an ISO type.

ok thank you!