Releasing SIN#

[Lee-Bee]

I'm in Ontario and have a BIN number to register my business. I have used the BIN number on tax receipts to parents for about the last 6 years, and said that the CRA can contact me if they need the SIN. I just didn't want my SIN in the hands of all clients.
I have had an accountant call and leave me a message asking for my SIN. My question is, would you release a SIN# over the phone to an accountant? How do I know for sure that it truly is an accountant?
Maybe I'm paranoid, but I treat my SIN very seriously/privately.
Opinions please???

I wouldn't give it over the phone to a random accountant that calls me. But I would give it to an accountant that requests it, leaves their name and number for me to call back. I would then use the name and number to look them up online and find their office and credentials etc before calling.