Wow, that keep... havn't seen a nicer one in my time on UOR. I could pay you in Bloodthirsty Bulls if you accept livestock. Concerning the marble, yeah it's a nice vendor spot, close to a gate and already well known. Of course every spot without spawn would be a nice vendor spot, if people did what people do on other shards: Gating and distributing runes.
Best of luck with the keep sale Gideon, it's been one of the most historical sites in UOR history... I still remember buying BoD's from there in 2012!.