I'll be speaking here of luna houses, but the same is true anywhere. First, its important to setup your vendor house the way your gonna want it to be, forever. You cant redesign with vendors up, and asking people to drop vendors so u could, will lose renters.
Its important to consider the shoppers view when decideing your design, and then where to put vendors. An open, first level, frontal, vendor area is always best. If you think about it, i know i personally prefer to walk down lunas street and say vendor look to open vendors to shop, and most do.
Now, to be a house people stop at regularly, you need to provide a few basics. My house always has repair deeds, spellbooks, runebooks, and such. Once these are covered, its equally important to have high end vendors, and everything in between. Diversity is the key, a wide variety of goods to look through makes your house interesting and fun for shoppers.
Finding renters is easy, with a little patience. A spam here and there over time will fill and keep your house full of renters. In fact just answering the crys in general chat is enough usually. The last thing you want is to turn people off by over spamming your house. I'd suggest limiting your spams to offering free vendors for specific needs - like maybe a marked runebook vendor, or a potions vendor. Just hearing you have space is enough if someone needs a space, and noone minds spam about free stuff.
Another aspect to consider is drawing in customers. You have your basics available, and vendors for them to browse, but aside from just passing by, what draws them to your house? A teleporter to the abyss would be great, but we cant all have that. I find that setting up a random vendor with whatever ive been scripting or farming, and selling that stuff really cheap draws people to check that vendor for daily deals. For example this week ive been doing heartwood a bit, so i vendored an oak saw really cheap, i have lotsa wood from an idoc so i put it on there...that sort of thing helps alot for the total house sales.
