Would You Trust a Stranger?

I had an interesting situation a short while ago that got me thinking - when did I stop trusting strangers? I just received a phone call from a really worthwhile local charity looking for support for a worthy cause.

I agreed to support the cause and things started getting complicated. To take my pledge, obviously the charity needed me to provide my credit card details, but exactly how do I know that the lovely lady on the other end was in fact legitimately from said charity and not in fact hired by fraudsters to collect credit card details? After an intricate dance in which permit numbers, ABNs and phone numbers were shared - I was still stuck. The phone number for the charity collection didn't match the businesses normal phone number I could see online, so even if I called her back I still had no way of knowing if this was legitimate.

I've had this same dance before with banks. Someone on the other end of the line claims to be from my bank and immediately pounces in with half a dozen personal identifying questions before they can share whatever it is they need to say. This is wonderful, except the same questions could be used by scammers to illegally access my accounts. When I ask them to verify they know something about me, they can't due to the bank's privacy laws. Checkmate.

Once when I insisted on calling the bank bank so I could verify who I was talking to first, I was put through to about five different people none of who had any idea why I was calling. Complete customer service inefficiency (probably) or proof my skepticism was warranted?

Now I want to open this up to the floor. How would you have dealt with this situation? Would you leave a worthy charity wanting to protect your finances or do you give people the benefit of the doubt? I'd love to know if anyone has any great tricks for checking if the caller is legitimate.