Hi Gareth,
I wonder whether your question 'guilty or not guilty' is only about stealing a mug you fall in love with... Anyway in my time I've learned that those kind of 'judgment' questions often hide more than meet the eyes. I've known seriously well-off people who stole out of boredom or for the sheer thrill of it. I've also known seriously poor people who stole to survive. I think we all know uber-rich who have built and continue to do so their wealth on stealing, cheating and conning their fellow humans. The likes of politicians, corporate moguls, etc. all of whom never get prosecuted. Unlike the homeless pinching food from supermarket or similar. In my book, it all depends on circumstances. Meaning - was harm done and if so who got hurt. The fact that you donated to the charity shop mitigate any potential harm the act itself may present. Does it mean I condone stealing? No. It means that nothing in life is ever simple enough to fit into the simple question - 'guilty or not' - regardless how appealing the simplicity of it might be.