I have enough troubles controlling my blacklist for the great deal of bot spamming that can happen in this game. I'd not be too keen on the idea of adding marketing harassment as a potential reason to block someone.

"Like, there's a retainer I'm looking at now called "Tigolbitties". Thanks, guy, and thanks, SE, for making me look at that. So clever."

If there is an offensive name or a name that'd break the ToS, just report them. It'd be same situation if it were a player's name. So regardless, you run the risk of reading something stupid. Giving the retainer's name, the listed item, etc, would be enough for them to link the owner for a report.