Just be honest.
Most NGOS are honest. But, unfortunately, many also aren't. As legitimate business is squeezed out by the damands for higher and higher profits by speculation, charities have grown as a source of outsourcing-and globalization-proof jobs- (along with 'national security', especially when its privatized, which has some similar issues)
They are one of the biggest rackets around in the US due to our "hands off" approach to taking care of the ever growing numbers left behind.
This is seen as appalling by Europeans and many others who feel that its the governments responsibility to do many of the things charities in the US are supposed to do. But disinvestment/services liberalization has meant that public services are being dismantled due to international agreements to let corporations have their turn, leaving nobody to help the poor.
This is because starting January 1, 1995, major limits were placed on what governments can do by the WTO GATS agreement, and they basically had to come up with a timetable and plan to end doing even that. ("progressive liberalisation" its called)
Despite the growing need, you'll find that too many well-established "charities" when it comes down to it, don't or even won't do important things needed to solve the problems they are claiming to want to solve.
If they did they often argue things like "they would lose their corporate funding", but the fact is, if government did its job, many NGOs would not be needed at all.
In the coming years, NGOs could be the main dysfunctional face seen of some real disasters by large portions of the American public, and as people in the developing world know, thats a truly awful situation to be in. Because there is ZERO accountability.
No matter how many trade deals they sign and how many services are auctioned off to multinational corporations, responsibility is ultimately demanded of governments (and if the electorate fails to pick up on something they do, it often ends up paying.)
Corporations are designed to shield investors and leave the public with the bill for their mistakes.
Even though corporations can have their assets sold off (but often only after they have been already stripped of assets and left a debt ridden shell) they can leave problems which cause massive losses to a population, as when the environment and peoples health is destroyed.
As you pointed out NGOs do also often siphon off lots of $$$. Especially in "emergencies". But then again, so do various "emergencies" elicit extreme levels of looting elsewhere. (see image below)