Ebay is not the be-all, end-all of internet sales. There are things which go well on ebay, and entire classes of things that don't.
Things that do consistently well are all items which have a large amount of personal value-added. For instance, most of the violins sold new on ebay are reasonably good (inexpensive) instruments (some are complete trash), but they are usually delivered to the end user in an unplayable condition. This is because the people selling them 1) don't know anything about violins, 2) don't know how to properly set them up, or 3) are chasing a commodity market based on price alone. The typical end-user has to take the instrument to a professional luthier, and spend $100 or more just to find out whether the instrument was worth the $50 he/she paid for it (the complete trash is basically expensive firewood).
I take violins which are a couple of notches up in quality from the typical ebay fiddle, and I set them up by properly fitting all the parts, and installing good strings, add a few accessories (including the "Don't Fret" fingerboard decal), all of which takes me about a half-hour per instrument (but I'm getting faster with practice). For that half-hour of intelligent work, I can sell my violins for around $200, or about 4 times what the unplayable commodity violins are selling for.
And the bottom-feeders can't compete with me, because they don't know how! They are trapped in a lowest-common-denominator commodity market.
On the other end of the scale is the guy who is trying to find the "secret dropshipper" that will allow him/her to sell stuff without maintaining inventory. This is a disaster waiting to happen -- you end up getting feedback based on how somebody else over whom you have no control treats your customer. Plus, you are completely at the mercy of whichever competitor (using the same sources) has the lowest IQ, and sells into your market with no clear idea of his/her actual costs (which BTW describes the majority of ebay sellers).
In general,
1) find a niche in which you are personally passionate
2) get good at it, and
3) sell large amounts of value-add into that niche
oh, and 4) keep the overhead as low as possible!