It's not an uncommon problem that people run into on sites like eBay. The problem is, you're not just just trying to compete with other drop-shippers on eBay, but you're also trying to compete against wholesale buyers and even wholesale's selling direct, so as a drop-shipper, you're always going to be out-gunned going up against the later two.
There is also the problem of other sellers using eBay as a sales funnel trying to direct traffic to their own site, so you can run up against loss-leaders. In other words, products being sold at either cost or below cost as a marketing technique by the sellers.
When you're using a platform like eBay to drop-ship, you need to concentrate on the slower selling items. Those items typically have the least amount of competition and large wholesale buyers, as well as wholesaler's themselves tend to not focus on so much, making it it a far more even playing field for small drop-ship sellers.