As a charity shop worker I have to point out the other side of the coin.
a) itI is a misconception that all charity shops are rates free. This depends on the local authority, and while some allow a small discount the councils are now strapped for cash as well.
b) items donated are all sorted and saleable items offered through the shop. In our case staff take their chances from the shop floor. Volunteers pay full sale price, or, if they want something we've put aside for recycle, they have to pay more than the recycle value. For example, if I wanted a book from the recycle pile I'd pay 10p where the recycle company pays us 5p.
c) We don't all know the value of everything. If we come across something (that might be) relatively valuable we will get advice (local jewellers aften value for no charge), put it out for auction, or, if we think we'll raise more money, offer it to a local dealer (I recently offered a local book dealer a couple of 1890's encyclopedias that I knew wouldn't sell and could end up recycled, he offered £20. Result for our charity
d) Our prices are low. Even so we still get complaints of charging too much as "it all comes free, and you're just greedy". Occasionally we get the 'good egg' who offers us more - WE never refuse! You can still get the buyer who sells on through e-bay or boot sale and delights in telling us so, but we have got the price we wanted and good luck to them.
e)We recycle clothes,plastic toys,soft toys,metal,china,books,stamps,mobile phones,spectacles,books,CDs,DVDs, (strangely enough Video tapes are not recycleable)
NB - I work for the local hospice shops, and it c osts £13 per minute to run, more than half of this has to be found by the fundraisers.
I could go on, but must get off my hobby horse and calm down.