Since sellers that engage in this sort of retail arbitrage do not announce that fact, eBay relies on complaints to identify such users. Until eBay cracks down on retail arbitrage, your best be is to avoid such sellers entirely if you do not want to risk receiving shipments from those retailers.
It may not be possible to always identify in advance those users who drop ship, but it is possible to identify some common characteristics of illicit retail drop shippers or other under-performing sellers, and thus avoid the worst of them.
Often they can be spotted by a combination of low feedback number, free shipping of heavy items, use of stock photos, high handling time (not necessarily if they are using Amazon, though), poor feedback received with complaints of delays and wrong items or out of stock cancellations, very odd item selection and/or quantities like items were chosen at random from a catalog, canned item descriptions scraped from another site, differences between registration location and item location (or vague item location -- like "US, United States"), or inability to answer even basic questions about the items being sold.
The sellers that manage to avoid those red flags are harder to spot, but also less likely to be a problem to actually deal with.
