You are the audit manager. You suspected that the company made some sales on special occasions but forgot to record them. The sales were made through normal processes and there was no breach of internal control. You asked your assistant how he would go about to find evidence either to prove or disprove your suspicion. He made four proposals:

(1) Confirming accounts receivable; (2) checking payments received after the balance sheet; (3) calculating gross profit ratio; (4) calculating inventory turnover ratio.

What would you say to him for each of these proposals?