I sell stuff that I order from ebay.. I don't do it in a high ammount of items, like usually 20 a month, just what people ask me and what I think its a popular item atm, i make around 60 euros in normal months but on June I made around 200 cuz of selfie sticks but I also made more orders from ebay that month than in other months.. its effective if you have money to start with and people to sell shit to .. or a local website like craigslist..
its ok to make some extra money but I know 2 or 3 dudes that started with this and then created an website to sell their stuff and they make an okay living out of it..