The problem with shopping in charity shops, is that you have to be the sort of person who buys clothes at random as and when you see something they like.
If, like me, your clothes buying is very focussed, for example I am currently looking for a good quality winter coat, dark grey, mid calf, unbelted, in a size 12, then the chances you will find exactly what you want in charity shop, unless you are prepared to visit hundreds of them, are, regrettably, very low indeed.
This not to say that I do not look round charity shops and occasionally buy something. If I see something I like, I am unlikely to buy it unless I can see exactly when and where I will wear it and whether it will fill an existing gap in my wardrobe.