In Canada, you can check to see if a charity is legitimate by checking the Charities Directorate on the government website. Legitimate charities are registered and have a BN number.
I checked the US gov page, and there is a "Search for Charities" link on http://www.irs. … ties/index.html.
I would not give money at the door. If the charity proved legitimate after checking the above, I would mail a donation if I liked the cause. Then you know it went to the charity for sure.