I have been involved as a volunteer with many charities over the years and you see the best and worst of people in every place. Bags of dirty - and I mean dirty - clothes literally dumped , actual broken furniture that they seem surprised that you cannot accept etc. When I am doing things on my own , I can use my own judgement, but when you are a specific charity shop you must go by their rules. Dont know if it is still the case, but the majority of charity shops would not accept electrical goods as they all have to have PAT testing, but Sue Ryder used to take them as they had people who did this testing and then they could pass them on etc etc. But working in the shops you can only follow the guidelines the charity set.
I am sorry you got someone who was rude and did not have the correct knowledge of the rules. This could be a variety of reasons
a. New person who had not yet learned the rules and did not understand how hard it can be to spend days in the shop. That you will not be lady bountiful handling beautiful things for most of the time, but lifting and sorting things and coping with everything from lovely people who do their best, to a whole range of situations , from people who are drunk or on drugs or trying to shoplift (yes even from a charity!) to antique dealers hoping to find something special which has not been recognised etc etc
b. Someone who is having an off day or is in pain and should have really not gone into work but there is no one else available.
c. Just as you say a rather rude person who should not be doing this sort of thing with the public, who will put people off helping your charity.
When I have run shops at times, certain people would be carefully given jobs in the back, and kept away from the public as much as possible. I did have one person that I had to say, very politely but firmly, not to be so pushy with the customers and she took offence and flounced off, but that is the only one I did have to specifically do this to.
However if someone has been rude more than once, I would try to contact the manager of the shop, explain what has happened and say that this person is not only behaving in an unacceptable manner per se, but will be putting off people from donating and could also put someone off ever helping that charity again.
In our area we have a community action group , and they are a great place to go to , in a very green way. They know all the local charities, and a womens refuge , and a "mens shed" where people can mend wooden things that are worth working with etc. so if I have something that I just dont know where it would be best used, I contact them and they will help to get it to somewhere that will be pleased to use it, and I am very happy to know that I am helping someone and also avoiding landfill etc.
One specific thing the PAT testing group can do is if someone has died and there are things like kitchen things, kettles, mixers , microwaves etc which have obviously been in use until the person has died, then these are tested and here I know that they have been given to people , such as young people leaving care and setting up their own place, women from the refuge, and someone not long ago who had had a fire and was without all the kitchen things. So if you look around and check with WI or local council or lists in the library you may find just the right thing that you need.
I am 79 in a months time, and when I look back over many long years I have been involved in all sorts of charities according to where my life took me, and of course there have been times when you could scream, or slam the door or whatever, but the majority of the times I have gone with no ulterior motive but to give a little bit of time. In return I have made lifelong friends, learned lots of things, been reminded that I have much in life to be grateful for, and when I am having a rotten day, in a lot of pain and not able to do much, it is good to know that I have these things to look back on.
Do keep on giving , for the greater majority of people you will meet will be decent and helpful, and you will feel happy that you have done what you feel is right.