a trader is someone who buys and sells financial instruments such as stocks, bonds and derivatives. A broker who simply fills buy or sell orders is not a trader, as they are merely executing instructions given to them.
Traders are either professionals working in a financial institution or a corporation, or individual investors, or day traders. They buy and sell financial instruments traded in the stock markets, derivatives markets and commodity markets, comprising the stock exchanges, derivatives exchanges and the commodities exchanges.
A merchant is a businessman who trades in commodities that he didn't produce himself, in order to earn a profit.
Merchants can be of two types:
1.A wholesale merchant operates in the chain between producer and retail merchant. Some wholesale merchants only organize the movement of goods rather than move the goods themselves.
2.A retail merchant or retailer, sells commodities to consumers (including businesses). A shop owner is a retail merchant.
A merchant class characterizes many pre-modern societies. Its status can range from high (the members even eventually achieving titles such as that of merchant prince or nabob) to low, as in Chinese culture, owing to the presumed distastefulness of profiting from "mere" trade rather than from labor or the labor of others as in agriculture and craftsmanship.