@cc, I think it is quite common for this to happen. Most of us like to think that our donations really good and that the shops will be grateful for them. However, the reality is that the shops are inundated with donations and cannot possibly sell everything that comes in. I make sure my clothing donations are washed and ironed if necessary and put other items into a bag especially for rags. However, I am aware that there is a possibility that not all my items will be considered right for this particular shop and that they might add them to rags or move them to another branch of their shops. This second option might be what has happened to some of your donations. As it is, any charity shop volunteer will tell you of the mountains of unsaleable, dirty rubbish that gets donated - some people have no shame. Also, unless there are designer items in a bag, if the items are from a smoker’s house and smell of smoke, they will pass them on to rags. Some years ago, a friend, who is a lovely kind person but who is a hoarder and lives in a very dirty house, gave me a bag of clothes to donate to my local charity shop. The clothes were crumpled and creased in a carrier bag and almost certainly dirty. A volunteer would have given no more than a passing glance before putting them in the rag bag. However, this particular lady was a high earning professional and the clothes were very good quality and wound fetch quite high prices so I washed and ironed them, much to the amazement of my then teenage daughter. I believe the shop was very pleased with that particular donation.
In a nearby town, there is an independent charity shop which sells books in aid of deaf and blind people. Most books are £2 for paperbacks and £3 for hardbacks, unless individually priced. The staff are very welcoming and always welcome donations, even bagfuls. I save my books l wish to donate until we make a visit to this town, as does my mother.