From a buyer’s perspective, auction sites can be a good way to find a specific firearm or an unusual firearm. You can cast a much larger net if you can look nationwide for that specific gun.
I went through my “black rifle” phase many years ago and I don’t see myself returning to that game. Much of the local scene caters to a younger crowd. So, for me, the auction sites provide a large store to shop in and lots of time to find exactly what I seek and not just what is in the display case in front of me. For example, a few years ago I went looking for a S&W model 640. Not a 640-1 or some other variant. That gun model was only made from 1989 to 1996. The odds of finding one in a gun shop near me were slim. And I could take my time to find a good example at a price I was willing to pay, even with shipping and transfer fees factored in.
From a seller’s perspective, I still think placing a firearm on consignment at a gun shop is the easiest method. It’s a win-win for the firearm owner and the gun shop. The item gets lots of exposure to people who are looking to purchase firearms. The shop handles the showing, the advertising, the transfer, and the money. Plus, the shop likely has the means to process credit cards sales, which greatly increases the chance the item will be sold. The shop gets inventory to sell without tying up money in that inventory. When the items are sold, the shop makes some profit to cover their time and effort. The gun owner loses a little potential profit in the consignment fees, but he also avoids the hassle of the FFL paperwork, showing/selling the gun. Plus, there’s a very well-defined transfer of ownership if that gun is ever used in a nefarious manner after the sale.
The next best option is placing the gun on someone’s table at a gun show. Again, the seller gets lots of exposure to people who are looking for that particular type of item. The potential audience of buyers is large, and people go to those events with the intention to buy something (not everyone in the crowd but there are buyers present). If your friend has a table at a gun show and he helps sell your gun, the polite thing to do is offer him some percentage of the profit, at least to defray the cost of the table. Depending on what state you’re in, (and the associated laws) this can be a good or bad method.
Much like Jeff H, My tolerance for stupid/dishonest, etc. people has diminished exponentially as I've aged. So even the gun show route has it’s limitations.