It is clear that the proprietors of the office, Mitch and Murray, blame the salesmen for the failure of the real estate business. The salesmen, in particular Shelley Levene, blame Mitch and Murray for providing them with weak leads. David Mamet presents these two cases without comment. On Mitch and Murray's side of the argument, one might point out that Ricky Roma still manages to close sales successfully. It is evidently possible to do so. However, Levene could argue that he was once similarly successful and still would be if he were provided with promising leads.
However, there is a third option, which is supported by the atmosphere of sleaze and desperation in the play. The system itself is rotten. A good product should not rely on high-pressure sales. Land is always in demand. As Mark Twain pointed out, they've stopped making it. There is something wrong with a system in which the salesmen have to rely on a range of tricks and slick sales techniques to sell something which customers genuinely need, which is probably the most substantial investment they will ever make, and which they should therefore be considering in a calm and reasoned manner. No one individual is to blame; the failure is the system's fault.