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The automatic sorting and counting process is rather noisy and not just the process of pouring the coins into the receptacle.
Maybe the customer is in a hurry, distracted, or didn't care.
The reject coins become fair game, first come, first served. 😄

Woo hoo! Just Scored a Loonie from a Compass fare machine today.

Now that's awesome! It's a nice tip just for being observant!