lcai

A broker puts the two counterparties together into a trade i.e. finds each party for the other , usually for a fixed commission .

The dealer waits for the two parties to come to him and collects a bid-ask spread from both together . i.e. he acts as counterparty to both parties. No commission is charged by dealer because he is paid the spread. To get to a dealer too , you might have to pay commission to a broker.