Which is why you incentivize salesmen via commissions and quickly fire those that are obviously showing up just for the base paycheck.
You can't really be suggesting that commissions are the silver bullet for aligning incentives, as if that hasn't been tried for thousands of years already, with very mixed success :)
Additionally, employees optimizing for pay/effort instead of max pay is still a win for the company so long as the employee brings in marginally more than they cost.