The vexed question of plates

I don't think this is a difficult scenario: Tuesday, I need lunch for 10 people, Wednesday I need lunch for 12 people. Corporate entertainment is a fairly well-established industry, I thought.

So, imagine my surprise:
"Hi, this is 'lets do lunch'. Just checking that as you have 10 plates from todays lunch, it would be OK just to drop off the two extra plates tomorrow. We'll assume that if you dont call back, thats OK".

Note the absence of a call back number or a name. So, yes, they wanted me to wash up their crockery so I could reuse it. Is there some plate shortage of which I was previously unaware? Perhaps a government initiative to reduce the carbon footprint of ceramic crockery?

24 hours later, and yes not only am I delivered food for 12 and 2 clean plates to eat from, they also collected and took away yesterdays ten plates... I despair of your species, dear reader. I'm starting my own.
(Hey, reproductive isolation is as good a definition of speciation as we have).