I agree that there are shoddy charities as well as charities which are well intentioned but inefficient and wasteful. I actually do some research and have to be satisfied that the money is being productively employed before I hand over my money.
In the case of the UNHCR I'm quite satisfied most of the money is going where its needed.
The UNHCR claims around 10% of its budget is allocated to admin costs with the rest of the money going into providing services for those affected.
I see no reason not to take them at their word. In any case they are audited and also receive large contributions from many governments around the world (e.g. the US gave $700m in 2011, Japan gave $200m, Australia gave around $60m) - so there is significant pressure for them to 'do the right thing'.
