Garage doors could be bought from stores such as Home Depot, Lowe's, Sears and The Big Door. Most of them do not take the old doors away unless you find a local store that does the maintenance works. They may be interested in the old doors.
a dealership is a business that buys/sells automobiles. A dealer buys/sells automobiles for a dealership.
It depends on where your from but the easiest place is eBay or any other website that buys/sells items.
newdiv
Consumer
Broker
investor
A stockbroker.
A person who buys and sells goods to make money is an entrepreneur. They have created a business that will hopefully generate profits.
someone who sells goods someone who sells goods Supply and Demand.
A slave trader buys or sells slaves
Stock trading.
A Stock Broker.