I might take a bit of flack for this, but I received a call yesterday identifying themselves as a professional fundraiser for a charity to take care of families where a member suffers from a particular form of cancer. While there are hundreds if not thousands of worthwhile charities that should be supported, the key piece is how much money from a cold call like that goes to the charity. In this case, it is 15%. The rest, 85%, ends up in the hands of professional fundraisers. If you look at a few websites, money for the cause should be 65% (rated a C by some web sites) to 75% or 85%.
In the case of yesterday's call, my reaction to 15% was to state that this was horrible and as quickly as possible to hang up without being too much ruder.
So, in the future, if you get calls from charities associated with law enforcement (in that case, it was 10% went to the cause), always ask. In both cases, I now have done so, I get a big pause before they'll provide the information. They don't try to avoid giving the figure, but from what I can tell, they realize that they're unlikely to get a contribution.