House Guillot is a noble house of Ishgard. Officially, they're best known for their well-bred line of war chocobos. Guillot chocobos, war and otherwise, have long held a reputation for being durable, brave, and obedient, making them highly sought after. Their black feathers are also unusually shiny compared to the standard, making them easy to recognize.
Unofficially, however, much of their wealth and power comes from more nefarious dealings. The Lords of House Guillot have something of a history with underhanded tactics, as well as skill with making their deeds difficult to tie back to them. Over the last few decades, they've come into several new businesses, shiny things, and pieces of land, having bought them up when their previous owners couldn't afford to keep them anymore. Lord and Lady Guillot simply consider this to be good business and nothing more. Ignore anyone who says otherwise, they will urge you, for their deals are fair and legitimate.
(If you think House Guillot won't chase away your customers and buy your business when it fails, then you are sorely mistaken.)
(If you think Lord and Lady Guillot won't gather some information or remind you that Halone Is Always Watching in order to get their hands on that land deed you were hesitant sell them, then they won't....if you agree to new terms, that is. Probably.)