Ask them. Any reputable company should be able to justify their costs. I work in expatriate tax, we frequently get people asking what things on their invoice mean/cover, almost every time we will explain what was carried out and the client will be happy and pay the invoice.
If they can't justify it, tell them that you won't pay it until they can.
Just my 50p
Expatriate - tax consultant dealing complex affairs of complex people in complex financial situations
Letting agent - too ruthless to be a used car sales man
I'm fairly sure the former would find it far easier to justify their fees!