I gave up donating to charity shops after volunteering for a well known local charity a couple of years ago. Every monday a van would turn up and dump stuff they deemed unsellable in their shops in a skip. Yes, some of it was junk but there were stacks of books, dvds, computer games, kids' toys and electrical goods that could easily have made them money. I'm not ashamed to say I rescued quite a few items for myself.
I stopped giving my time and money altogether once I'd seen first hand the unforgivable squandering of money that had been given in good faith.