You know the old saying that money is the root of all evil? I think that while money can and is often used for a lot of good - for example, sterilising cats! - the use of money can always be a bone of contention.
When money comes into the equation, situations always get thorny. Very well-meaning caregivers have been known to fall out when money is involved - and often there isn't any dishonesty or ill intention involved.
I have seen groups fall apart, and caregivers unable to work together because of misunderstandings over money. Often one caregiver decides to help out by collecting all the money and making arrangements to spare the others problems. Some miscommunication occurs, and then people start accusing each other of being dishonest or of stealing money.
It's very difficult of course to avoid any miscommunication, but especially when money is involved, it's best to be as above board as possible (easier said then done!). People are often willing to forgive a lot, but when money comes into the picture, the taint of dishonesty sometimes never washes off.
At the same time, I think it's important to try and realise that the majority of people are working to help the cats. This does not mean that one should not be vigilant or query anything that seems strange, but with the majority of volunteers working and being busy, sometimes things do get overlooked.