Do you have any figures to back that up? Most charities here in the UK publish their expense ratios (i.e. how much is spent on admin, fundraising, on the actual good cause etc.) and they tend to be fairly efficient.
Expense ratios for Internet Archive:
Programs: 88%
Administration: 10%
Fundraising: 2%Now clearly this works: they are raising more money this way, but the side effect is that people like me refuse to give to a charity that hassles me every time I go to the supermarket, and spams me every time I give them money.
By the way, I had some trouble figuring out the right term to put into a search engine. Turns out the industry term for this is "face-to-face street fundraising". And in the UK it's sometimes called "charity mugging" or even "chugging", which you have to admit is more amusing than going straight to Godwin...
Even if they're an agency, the ones I know of are paid hourly, not per sign-up.
http://www.charitynavigator.org
My takeaway is that there are plenty of large charities that spend more than 90% of their revenues on their mission and plenty that don't. For me, the big ones that do 90% makes it hard to feel great about a smaller charity that only hits 70% (but then I am a crank that dislikes solicitation).