Hmm, from my imaginary buyer's point of view I don't see how much it will cost to add you as an intermediary. Fixed rate? Percentage? I mean I signed up with my Google account but then was asked to give my phone number, and... yeah that's about where my own drawbridge tends to be commonly raised, especially when I know so little. So I aborted. I mean my instinct said that maybe if I were really interested in a property I could just, like your site mentions, send a message to the physical address and then if that didn't work maybe come back and give out my personal number, maybe even after looking online for the owner. The site looks nice btw.
I don't have statistics, but I guess a home is sell once every 20-30 years, and is in the market for 3 months. So if I sell a cold offer to buy it, there is a 1% chance that it's on sale or the owner is wiling to sell it.
Most home sells have a reason, for example the owner died and the children and selling it, or the home is too small because they have a new children or too big because they have an empty nest. So outside the period it's in the market it's very difficult to convince the owner to sell.
Selling a house involve a lot of taxes and commissions, like 15% here in Argentina, perhaps more. So if I have to sell my home without a good reason, the buyer must pay like 20% more to cover all my fees and taxes. Add the fuss of moving (1 week to package, and 1 week to unpackaged, does the house need painting?), looking for a new home (1 month), smiling to the real state agents that while they try to screw me, discussing with my wife because she likes another house, crossing the finger because the new home can have the plumbing made of painted cardboard, or a very noisy neighbor, or a crazy neighbor, ... so to convince me to sell my home in a cold offer, you should add a 50% premium to the price.
With a 50% more of money, the buyer can get a better house, or have a lot of freedom to fix other house.
Don't know in the US but here in the UK the vast majority of people sell through estate agents. If you're looking to buy then you give your details to estate agents so that they can contact you when something comes up.
Now if you find a house that you really like then it costs nothing to leave a card through the letter box. Still, I guess homeowners might be a bit suspicious and not comfortable going alone without estate agent (if they'd consider selling at all)
Google offers a free multivariate testing suite.
You can form hypotheses, but without testing these are only guesses. Consider talking to users who land on your page. There's no substitute for talking to actual users. Typically a live support chat box is used for this purpose.
Get professional help:
like the idea, like the site.
you need to find home flippers, i would guess.
Let's see if I get this thingy right:
1) you have a database of homeowners (possibly public data) and (somehow) their e-mail addresses
2) for a fee you give this address to a user
3) the latter can thus cold e-mail the owner asking if he/she wishes to sell the house
So, if the thingy catches, homeowners of nice houses in good areas (and that have no intention whatever to sell their home) will be spammed by strangers.
BTW - and IMHO - the "conversion rate" of 90% opened letters are seemingly meaningless metrics (unless we have some comparison data on how many people opens "random" letters they receive), it would be interesting to know the "conversion rate" of letters actually leading to a sale.
Maybe it is a US thing, I wouldn't even think of sending letters to perfect strangers telling them I would like to buy their house (and possibly making an offer for a house I have not even visited).