On Pacific I have 2 Vender Houses and 2-3 Venders at each house. I did not realize that there would be so much maintenance. About once a week I need to go Spam at Luna Bank to let people know that I have Vender Spots for Rent. There is so much turn-over. Sometimes I lose about 4-5 Venders a week. It seems like contant juggling to make sure I have Vender Contracts in stock. The pain is when people need to reclaim their inventory from the House Sign and then I need to replace their Vender (I tell them to put a 1 Million Gold Piece Check on your Vender and have a friend buy it) or they forgot all together and it goes into the Moving Crate. On the other hand, what goes into the Moving Crate is now mine and I have received some pretty nice items from forgetful venders. My philosophy is this: If you do not have time to check your Venders at least once a week, then you have no business having a Vender at my House.
On the other hand, Paulonius is correct in saying that you need to sell "What is Hot at the Moment". Right now, it seems to be the Imbuing Ingredients, especially Crystalline Blackrock and Relic Fragments. Also Oak Boards, Mining Gems, Balms and Lotions including Gems of Salvation...
Having a Vender is a Love-Hate relationship -- Ihate doing it, but love the gold that they give me...