$[$ Select $]["$Brokers$",$ "Market makers", "Bookies"$]$ match buyers and sellers and take no risk. They earn $[$ Select $]["$commissions$",$ "bid$/$ask spread", $"12$b$-1$ fees"$].$ Market makers buy and sell from $[$ Select $]["$an IPO", "retail investors", "their own inventory"$]$ and for the risk they take are compensated by $[$ Select $]["$commissions$",$ "bid$/$ask spread", $"12$b$-1$ fees"$].$