@kpnuts
What your friend says will certainly be true for charity auctions. That is auctions that are specifically held for a charity or charities. That is because the people who turn up to bid are there to 'give' more than to buy, and some of them will be virtue signaling to others in the group. A regular auction is a different crowd, and most bidders, in the auctions I have been to, are traders who come to buy and then sell on at the best profit they can get. Occasionally you get 'over enthusiastic amateurs', as they are called in the game, and they might bid higher for charity, but only if there are two of them in the room bidding against each other.
Finding charity auctions may be difficult. There is a website
https://www.ukauctioneers.com/ and you could try contacting them and asking if they know about any charity auctions, or where else you might ask. The only other thing I can think of is to wait for Red Nose Day, find local organisers, and see if you can organize a local auction for people's unwanted items. Maybe a local auction house would be willing to assist in the process, as it could be good PR for them.
Sorry I can't be more helpful.