I've always wondered if it would be a possible business venture (in the US anyway): have an establishment that offers to sell locally people's used PC parts and then take a % commission from the sale. Kind of like a broker but for PC parts. I know I'm one who would seriously consider it for convenience and in the case of meeting up with a stranger for a sale on Craig's List, safety. Haggling by the buyer is another pain.
Say for example someone wants to dump a GTX 970 for $225 and a potential buyer comes in and offers $215. If the 970 seller agrees, it's an easy $10.75 made with say a 5% commission for the business. Just looking at my local metro city's Craig's List ads for PC components, there are thousands of dollars worth of items for sale. And that's just parts, not the used PCs and laptops also for sale which could be an expansion opportunity. There is nothing here in my city (Atlanta) that has that type of business.