I know of a wholesaler i can make a profit on but have only sold things i found around the house on ebay?

it took me a long time to list each one of these items i have done reserch and can sell up to 20 items a day even more if i have the time as i see other sellers doing this how is it posible for these sellers to list all these items and take them to the post office in one day and also deal with returns