Find the value of your used appliances by evaluating their condition, comparing the market prices and averaging the available data. You should also leave some room for negotiation and determine the lowest price you're willing to accept for the appliances.
First evaluate the appliances and note down all dents, scratches and loss of functionality. If there is severe damage, you can replace the corresponding parts and add the cost of replacement to the final price. With the appliances evaluated, check listings by other people. When possible, make direct comparisons to the exact same brands and models.
Average the price data you gathered, factor in your evaluation results and decide on the final price. Depending on the condition of the items, adjust the prices to be above or below the market averages.