Aside from selling exclusively online or via a flea market (both are good ideas), another idea is to be just a middleman and sell used items to antiques dealers, etc. Pro: you don't have to worry about the retail end. Con: you will get less for your goods, because the buyer will need to mark items up to re-sell to the end consumer.
Other options get more expensive. But here are two options to consider:
Option: an antiques/collectibles mall. If you sell items that are considered antique, vintage or collectibles, they might fit in with an antique mall when you rent a display cabinet or floor space. Pro: you don't have to be there during mall hours to man your booth -- mall employees handle the sales. Con: the antique mall option can get pricey.
Another option: sell at antique or collectible shows. Again, it all depends on the types of goods you sell and how much you are willing to pay for exhibitor fees at shows. Pro: you can do this a few days out of each month, not all the time. Con: it can be expensive and involves long working hours during shows. Some people don't like the long hours.