This scam will actually work with alot of people. I've seen someone else doing this in the fm, and i traded just to see how he did it. what he did was put in 25,555,555 mesos ( i had illbis to sell to him ). he'd trade, and cancel right after, and then type that i was too slow
I'd re-trade a couple times, and once i accepted, it was unsuccessful because he had no room. Then he must've used 1 potion taking up a space in his "Use" inventory, and thus creating a slot. He'd then say try again, or 1 more time. This time i knew he wasnt going to put in 25,555,555 mesos. Instead he put in 2,555,555 mesos, and accepted.
theres an example if anyone didn't understand how this scam works.