Dealer deals with such goods which requires large area to be covered and distribution of goods to different areas,places of the country on a fixed price marked on the products by the manufacturer where goods passes through different stages and sales process i.e. from first stage of manufacturer and finally reaches to the end consumer for example all generally home provisions/ consumable items.
whereas Trader deals with such goods which are raw-materials or materials in nature procured from the manufacturer and sold in the market by the trader on profit basis .
In my experience in the U.S. hand tools, automotive aftermarket, and hardware industries, a retailer is anybody who sells directly to the consumer from a fixed location. A dealer is somebody who sells to the consumer, and buys from a distributor. I've never heard of a trader as someone who sells to a consumer.
Here are a few places that would sell automotive tools like oil filter wrenches:
Retailers generally sell to the end user. eg. a Amazon is a retailer in that it sells directly to end users.
A dealer is usually an intermediary between manufacturers and retailers (or buyers and sellers). eg. car sales, real estate agencies.
Trader is used in two ways. The first is as an entity that buys and sells products for profit (and generally only holds them for a relatively short period of time). Think stockbroker, wholesale importer, etc.
Trader can also be used as another word for retailer (at least here.) For example, the local trader's association is the association that represents all the retailers in the local high street (or mall).
Our view of it is a dealer or trader primarily interacts with the wholesale side of distribution. Perhaps the trader manages import/export of said products from the manufacturer. The retailer usually is the one selling to John Q Public and collecting sales tax. However I do not think this is a standard and can be viewed in many different ways.