In regards to the question concerning online auctions, this post is more about having been in the role as a seller (recently), although over the years, I always have been a buyer. Thus I have been in both roles.
I recently consigned a significant portion of my collection to Gateway Auction of Chambersburg Pennsylvania. They offer about 4-5 train auctions a year, and do so within a combination of in-house bidders along with Invaluable, Hi-Bid, and their own virtual bidding platforms. I monitored the progress in the days leading up to the sale..... the activity on all three platforms. Just hours before the sale, what Gateway did was merge the highest bids from the three platforms, and the highest pre-sale bid becomes the opening bid for the live sale. Having attended in-house as well as participated virtually in quite a few auctions, I was always very satisfied to Gateway's standards of professionalism and ethics. Yes, there is both a buyers and sellers fee. But when I think about their costs and the effort required to prepare for and execute a sale, I think it is pretty fair, and overall pleased.
In regards to Stout, I think they also do a very good job, and are very professional. They too have both buyers and sellers fees along with the shipping and packaging costs. I have purchased a number of items from them in various sales over the years. But a couple of years ago I approached them with the possibility of consigning my fairly large collection segment to them, and not only were they somewhat dis-interested, but they never got back to me. That is when I thought about looking into other auction providers.
And by the way, I recently compared some of the more desirable items in my recent sale with the same items sold in a Stout auction, and actually some of my items sold higher on Gateway than on Stout. But other items sold for less. So, I think this is a function overall of "who is either in attendance (both virtually and in-house)" and what buyers are looking for that day, than maybe the auction company. And, there are probably quite a few resellers (looking for items that they can purchase and resell with the margins of a profit) in attendance as opposed to just a private hobbyist or collector.
I also have found that if one is using Greenberg and eBay as standards of "comparative worth", you can easily see if you have done quite a few of these online sales, that buyers are normally pretty sophisticated in knowing and determining the ceiling price, as they are" plugging in" the buyers fee plus shipping costs, and for the most part, will pretty much "shut-down" their bidding when that ceiling is reached.
Anytime that I have been in the role of a buyer, I constantly try to remind myself while actively bidding what the buyers fee adds to the bid price, and how much shipping fees add to my "walk away" buyers price.
And having read the thread up to this point, it is fair to say as a buyer, you always want to buy at the least price point possible (inclusive of fees and shipping if you are not in attendance). As a seller, one wants to sell at the highest price point possible inclusive of fees. I guess that is true of trains but just about anything
Hope these thoughts contribute to the conversation.
Chuck