I have sold a few things (mostly used fine to excellent condition guns at great starting prices) at GunBroker.com and at AuctionArms.com (more at GunBroker.com). I have also bid on a few things on each site but, I don't think I actually bought any firearms via either of them if only because I did not have the winning bid. The prices were not competitive enough for me to buy them online as opposed to buying locally.
Even though I have sold only a few things, as a private individual not as a dealer, I can tell you a few things about buying/selling on these sites. First off, think of this: Why would anyone want to buy a firearm through one of these sites unless at a fairly exceptional price? I can go to a local gun store, a sporting goods store, or a superstore (like Walmart) and pick up a fair to great deal. Let's say, for illustration, I can buy a Scheimzerzinger Volksgun in caliber .777 super magnum in a gun store for $399.99 plus tax. I go to Walmart and they have it for $329.99 plus tax. I go to the sporting goods store and they have the same, in a hunting season sale, for $309.99 (yes sometimes they under price even Walmart on Scheimzerzinger Volksguns).
Now you (any dealer, especially a new online dealer, in general) come along and want to sell the same rifle on the Internet by way of GunBroker.com. Why would someone buy from you instead of one of the above retail establishments? It certainly would not be because of your online selling reputation, you said you are about to do this. Would it be because of price? For what price do you think you can offer this gun? Would it be less expensive than it would be at the Sporting Goods store or at Walmart? OK, so you decide you will sell it for $20 less than the lowest of the above prices. Then you also have to add on shipping. OK, let's say $18.00. You are still $2.00 less expensive. Then you have to add on handling. Please don't tell me you would not charge for your time, your packing material, and so forth - because if you tell me that you will never make any money if you mean it. Even if you don't charge for handling would there be other expenses for which you would need charge or for which the buyer would have to pay even if you did not charge? In my state I am required to pay sales/use tax on items I buy over the Internet in the event the seller does not charge me accordingly. Once this was not made much of but now it is very serious. My state even now sends out the paperwork with the yearly income tax forms. In my area of my state that would be 8 3/4% tax. Still you are $2.00 less expensive because the stores would charge the same tax but, that is only if you don't charge handling; I mention this only so you don’t think that by buying from you they do not have to pay tax. I would get the better deal from you or so it would seem. Yet, if I buy at a gun store or sporting good store (maybe even at Walmart) and, I want to bring it back because it is faulty - they will take it back. You say - "so will I"; and that is fine but who pays the return shipping - not you I would bet! I also get to actually see and hold and work the actual gun I will buy at any of the above stores. I do not get that buying over the net (unless the guy selling is local and agrees I can stop by for a look). I also get the firearm immediately when I buy it at the store; with online sales I have to wait at least several days before receipt, this in addition to waiting for the bidding to be over (or even the buy it now process), waiting for you to contact me that I had the winning bid, waiting for you to send it and so forth. Then there is also the issue of trust. I can pretty much trust a sporting good store or Walmart to stand behind their items. I can trust certain gun store owners too. When I buy over an Internet auction house, that trust is not the same - nowhere near the same. Oh and did I forget that other expense? No not really, I just saved it for last, the cost of the FFL transfer. if you sell me a rifle interstate, then I have to have an FFL dealer handle the paperwork before I actually get my mitts on it. In my area that would be anywhere from $35.00 to $75.00 (less expensive in other areas but usually not below $25).
So, even if you sell the rifle so the overall cost would be lower than at a retailer, there is that waiting and the not knowing anything about you (except for your feedback) that would make buyers hesitant to buy at your price. Breaking into business selling over the Internet is bound to be as difficult as breaking into the retail business in a storefront - even for someone who already runs a gun shop. There is a lot of competition out there. The thing is though, the cost is minimal compared to a gun sore. No store rental, no electricity (well some but only enough to run the computer), no employees, no insurance for the store but, you had best get some sort of business policy covering selling guns.
This is not to discourage you, just things to think about. Apparently many people are at least supplementing their incomes by selling guns online. Good luck to you.