OK, now I understand more clearly. I do like the niche aspect of the idea personally, however that's probably it's biggest negative as well. The problem any new start up auction site has is generating traffic, without that traffic flow right from the start you some how have to inspire sellers to spend their time developing new listings for the site, not an easy thing to do because it's an unfortunate fact that most online sellers tend to be lazy and won't usually take the time to worry if they don't see any potential of an immediate pay off.
That's one issue., second one, and probably even bigger that that first is the actual size of your market. Developing a niche auction site, mush like a bidz,com or similar, you're limiting the amount of potential customers, selling customers that is. With just mobile phones, even though everyone on the planet has one, you're really aiming and a very small section of sellers over all.
Even if you can find the sellers to join your site, how many will be selling the same thing as the next with dropshipping. Yes, it's the same on eBay of course, but you may attract a higher number of dropshippers than wholesalers and just private sellers on start up and that could cause some issues.
Have you thought about slight widening the market, maybe going down the road of Total Tech, so phones, tablets and so on. Still has a niche feel about it, but gives you more customers to target in regards to selling and more appeal for buyers to jump on the site as well. My suggestion would be looking at those points and see where they take you.