I think the fee you're charging is too low to attract the number of sellers you're looking for. Based on the trades that occur on LocalBitcoins.com, buyers are willing to pay 5%-10% above spot in order to buy bitcoins via bank deposits.
If you charged enough to pay the seller 2% above spot, it would be worth their time to provide a steady supply of coins for sale because then they could use the deposited funds to buy more coins on Coinbase (1% fee) and recycle those back to your site.
You sir, are reading my mind. I love being able to offer bitcoins to buyers at 2% above spot. I think it is about as good of a deal as can be found considering the timeframe for funding, ease of use etc.
Yet I also know that there are people who would trade off an extra few % points to have access to greater amounts of bitcoins any day of the week.
Now just for the sake of argument...this is just a hypothetical situation (caveat caveat caveat). Is there a world that exists whereby the existing framework which is offered at Bitcoin-Brokers can coexist with a second tier service?
When I say second tier service, I mean a premium is paid to the sellers to open up either a predictable arbitrage opportunity, or simply enough incentive to encourage additional sellers to opt to make use of the service. Considering that sellers could sell and effectively be paid in cash the minute the sale occurs, what sort of framework do people need to see to open up a recurring predictable profitable arbitrage environment?
Perhaps like a hybrid car which offers both, and each one kicks into play under different supply versus demand moments with the buyer always having the option if they wish to buy or not.
For example, lets assume that there are 100 bitcoins listed for sale at Bitcoin-Brokers which can be purchased at current rates, just the way things work right now. Once and only once all of those bitcoins are sold, do the second tier bitcoins become an option for the buyer. The sellers who insist upon being paid the premium will not have any of their bitcoins sold until the first tier sellers have sold theirs first. Once those first tier bitcoins are sold out, under the way the business operates right now, no sales can occur, afterall, we are sold out.
Hey...its Saturday and its raining....the mind wonders these sorts of things over the first coffee for the day.
PS-Bitcoin-Brokers would still only take a 2% fee, so don't worry, this isn't the early hints at a rate increase.