Virtual Assistant here! Although I do not specialize in real estate.
It would really be in your best interest to find someone with a niche for real estate. And there are many out there, they go by the name "Real Estate Virtual Assistant".
There is a website called
www.revanetwork.com. It's a membership organization and there you can find a Directory of those VA's who specialize in real estate.
Also, try
www.virtualassistantforums.com. It's a very active bulletin board with VA's from all over the world. There is a board for REVA's and you as someone looking to hire can also put a request on their site.
I'm not sure of the pro's or con's of going through a VA firm. It seems like you may end up paying more since it's a subcontracting situation. If you were to post something on the board I mentioned above, I bet you would get all sorts of responses and you can start to determine who would be your best match. I am pretty sure that it is a free service.
There are many people out there starting businesses as VA's but don't truly have the skillset, which makes it more difficult for those of us who have a good thing going. So many people want to work at home (for good reason!), and so they open up shop but really don't have a grasp. You want to be sure and see some testimonials, see some examples of work they've done (if possible!). Maybe even see if you can contact one of the VA's clients.
OP - if you need any other feedback, just PM me!

Best of luck!