Well, as I suspected, my call to submit positive tips for growing your eBay sales received mixed responses (although I did appreciate the "Thank you card in the package" tip). So I thought I would share a few tips of how I reached $1,000,000 in sales, mostly selling on my own.
1) Know your market. Before I go through the trouble of listing anything on eBay that I haven't sold before, I research the market for that item. This has saved me countless hours of frustration and time wasted on selling low value / low demand items. If the item doesn't have a recent sell through rate of at least 50% and/or isn't selling for a minimum of $25 or more, then I don't bother with it.
2) Begin with the end in mind. 95% of what I list on eBay is sold on consignment (which is another conversation entirely,...). Before I accept an item, I mentally ask myself "Is this worth my time to sell this on eBay?" For example, selling a pair of vintage speakers for $100, that will take me 20 minutes to test, another 20 minutes to photograph and list, and 40-60 minutes to pack and ship. This is NOT worth selling on eBay. They're heavy, labor intensive, and don't sell for a high-enough price to be worth the effort.
Likewise, when someone mentions that they have a nice pen collection to sell, I am more than happy to deal with it, as they're small, easy to process, and take little effort to pack. Over time, you should cultivate a list of what you're willing to sell / not sell with minimum values attached to genres that require extensive evaluation or packing effort.
3) To make more, compete less. One of the reasons I greatly prefer to sell older items over newer items is that is there is a much smaller supply of older items, which can sometimes result in much higher demand. For example, if I were to try to sell the newest Holiday Barbie, I would first have to find a reasonably priced source, then sell my product less than everyone else in order to move a significant amount of volume of the product. My profit margin would be squeezed due to all of the competition that is selling the same item (not to mention that it is seasonal).
However, if I were to source vintage Barbies in good condition, I would probably have a harder time finding them, but my efforts would be rewarded with higher prices realizes and less competition. Plus, there is good demand for the item year round.
4) Learn to sell at auction. One of the most prominent features that eBay has over other selling platforms lack is that it allows sellers to sell items at auction in addition to fixed price. Auctions allow sellers to sell a high quantity of items in a short amount of time, due to the limited purchase window they present to the buyers. Additionally, if you have an assortment of similar items to sell and you structure your sale right, then there's a good chance that buyers will make multiple purchases if they can save on shipping costs.
Auctioning doesn't work well for everything (it's better for hard-to-find items instead of everyday purchases), so be sure to study the market for your item beforehand to determine if it's a sales strategy to incorporate.
5) Don't take it personally. Stuff happens and people are annoying. That's part of selling online and/or running any business. As frustrating as it is to have things lost by the post office or dealing with difficult buyers, it's simply the cost of doing business. Work to resolve the issue as quickly as possible for your own mental health and make a note of what you would do differently in the future to minimize having the problem again.