I see a lot of people talking about how SE needs to implement measures to make sure that this sort of thing can't happen to begin with. That's a good line of thinking. SE should implement measures to make trading work like things such as party/LS/FC invites and loot and the like. I think what everyone who is arguing that it's not worth the time and effort of reporting is missing, is that if this type of behavior isn't reported and brought to the attention of GMs as being something that can be abused, SE won't notice that it is something that needs to be fixed. People arguing against reporting griefers who use this tactic, I would ask you to consider that reports of this nature are used for reasons other than just handing out punishment. Reporting things like this also help bring unintended mechanics/uses/exploits to the attention of the development team so that they can find ways to deal with them and make the game more functional and enjoyable for everyone.