When Haman collected 10 trays and dropped 2 trays, he was left with 10 trays - 2 trays = <<10-2=8>>8 trays.
When he added 7 more trays, the total number of trays became 8 trays + 7 trays = <<8+7=15>>15 trays.
Since each tray contains 36 eggs, the total number of eggs to be sold is 36 eggs/tray * 15 trays = 540 eggs.
#### 540