Before you make a contribution to any organization it is wise to know who they are and what they do. No legitimate fundraising effort is so urgent that if you do not make your contribution right at that moment someone will suffer. A day or two or even a week is not going to make a difference. So take the time to research.
There are a number of websites where you can check the status of a nonprofit. It only takes minutes but allows you to feel better about your donation. GuideStar.org requires that you sign up for a free account in order to receive very detailed reports on organizations. CharityNavigator.org provides a limited amount of information without a free membership. More detailed information is available to members. The Better Business Bureau has been around for decades. They provide free information that is easily digestible at a glance.
The bottom line for charitable giving is to trust your instinct. If a solicitation sounds too smooth or vague, be suspicious. Think of charitable giving in the same terms as international diplomacy, Trust but Verify.