I agree with a lot of what you say, TinSoldier, and would add that the idea that charity shops are doing people a favour by taking things off our hands may heave been true when they would collect, or would accept assorted goods and sort through them themselves is a bit outdated. That used to be true, but now, for all sorts of reasons it is not the case. My High Street has a few charity shops, but none of them collect, some won't take books, others won't take electrical items. None take furniture, and so on. Two have specific days when they will take donations and turn them away on other days. Some want clothing sorted into types, with shoes paired and clipped together, and so on. I am fully aware that there are operational reasons for the restrictions, but a combination of them means that donors can't easily follow the advice of decluttering and simply bag things as 'chuck', 'keep' donate'. They have to be carefully sorted, taken to the shop (not necessarily easy for those without cars or shops with parking near enough to lug heavy bags) and timed to arrive on particular days with specified goods.
Donating is not as easy as it was, and as has been mentioned, there are other outlets for better quality items. The decision is with the donor as to whether giving to a shop is going to yield more than the profit on a Vinted sale. Knowing that there is a good chance that the items won't even make it to the shop floor might not be a consideration if you only want the things out of the house to save you going to the tip, but if you really want to help the charity it is not unreasonable to assume that they will be sold at whatever the local market expects for second hand goods.