I agree with Meryl Streep about the need to be selective in terms of only donating quality items with a high probability that someone will want to buy it, particularly as many charities are short on volunteers to check sort and label and serve in shops at the moment. Mini skips are anything from around £120 to hire for a week and people should not expect to use charities as rubbish collectors. If you intend that the proceeds of sale are to be used for charitable purposes, you also need to check whether the charity itself will be collecting and selling the items and reaping the sales receipts ( and potentially gift aid) or whether the collector of the goods is a collection agency that simply collects and makes a nominal donation of around 20p a bag to the charity and who then trade the donated items for profit and resell the choice items on ebay or other outlets. Sometimes the organisations that do this do make it clear that only a nominal amount is going to charity but others are, I feel, deliberately vague about the distribution of proceeds of sales and the private profiteering.