Never been in a snobby charity shop in my life. Even in a local town where a row of charity shops have designer clothes and exquisite accessories, I have never met anything but really friendly people running them. I bought a beautiful 1960s Jaeger linen dress there for £40 and considered it a bargain.
Try comparing the rise in charity shop prices with the rate that prices as a whole have gone up. You will find that they they are roughly in line. When books were 6d in a charity shop, a new paperback was 5 shillings. Now, when a new paperback can often cost up to £10.00 or more, £2 for a secondhand one seems quite reasonable.
The reason Charity shops do not sell visibly worn clothes is because there is little or no demand for them. Most people will simply not even consider buying a garment that isn't in really good condition. So there is no point in a charity shop keeping such garments, so few customers want them. The same applies to china, glass, bricabrac. We run a small antiques stall and we have found the same thing there. No one now will buy a piece of porcelain, no matter how pretty, if there is the slightest chip or small hairline crack. Once there was always someone keen to buy such pieces because they were so much cheaper.
Individual charity shops know what they can sell and what they can't. I recently took a whole load of stuff to a charity shop. They didn't want 2 rugs 'because rugs do not sell' and they didn't take the books, because they had so many in the storeroom. That struck me a eminently reasonable. So I went to a shop in another nearby town, who were absolutely delighted to take all my books. The rugs, DS decided to take.