Thing that happen almost every day:
Agent: Could you give me the machines serial number?
Customer: Why do you need that? cant you just look up all machines of <company name that probably has 100 machines. And we don't even have access to such lists)
....
Agent: You need to open the door at the left side of the printer
Caller: I see the toners and stuff (Means he opened the front door)
...
Customer: The machine won't print, you need to send out a man
Agent: Are there any error messages?
Cu: Yes, replace toner NOW (toner at 0%)
---
And a one time occurrence:
Customer: I need toner for <competitor brand printer>
Me: I am afraid you have called <our company>, that is a <other company> printer
customer; But I have ordered their toners here before!
(Yeah, likely...)