I've been selling items on eBay for about a year, slowly building a business.
When I started out, I thought price was everything.. and was looking for those "miracle" sources online... well they don't exist. Perhaps at tradeshows and through trade magazines, but I haven't gone through that yet.
The fact of the matter is, if you are drop shipping or buying in light bulk wholesale then your profit margin will be small.. but it is possible to make a profit -- in the upsell. People will pay a premium and give you an ok margin (considering your risk is nill with dropshipping) in the upsell. You need to be selling products that are either little known, or creating unique product bundles. I don't worry about what Amazon.com or other sites sell my products for.. if your customer was looking to buy from Amazon.com then they would be on Amazon! There's no reason to care just because someone was too lazy to look around for the best deal.
That being said, I never sell at a loss on eBay, and most of all I try to never undercut the competition. I do occasionally have low bid auctions, but I set my buy it now price at a premium to other sellers, and I usually get it.
You simply have to list, test, and eliminate unprofitable products. It cost very little of your time to "test the market" on eBay. You just need a few small repeatable successes.
Also, I highly recommend you have different accounts catering to a specific niche, preferably with your username equivalent to your .com.. although the recent eBook changes have made it alot tougher to build feedback.
In summary of this long winded post:
1) Accept that you will have tight profit margins from dropshippers or light bulk wholesalers.
2) Sell lesser known products or create unique products.
3) Upsell like crazy.
4) Never sell at a loss or undercut the competition. Forget about competing with anyone on price.
5) Eliminate products that don't work out, and keep trying new ones.
6) Different accounts is good if your username matches your.com