If you have a knack for knowing when an item has potential value, and like the ebb and flow of business then have I got a potential line of work for you. There are actually people who make their whole living by buying items at flea markets, Hollywood pawn shops, garage sales, craigslist, etc. and selling those items for more.
This only works because people are frequently trying to get rid of what they consider to be junk without knowing the real value. Take old stereos as an example. There are loads of people who collect antique audio equipment (they swear it sounds better) and sometimes will shell out top dollar for even the parts in old amplifiers, speakers, etc. So a person may find a real bargain in a thrift store and be able to sell that piece for hundreds online.
Personally, I have a friend who does just that. They are constantly out and about hunting through these types of venues in search of hidden treasures. The trick is knowing if there is a market for such things.
That’s where having a smart phone comes in really handy. One can easily and quickly look up what an item can be sold for while on-site and decide if it’s worth buying or not. While you need to have a good eye (or you’ll be looking up items all day) to begin with, you can quickly learn what sells for good money and what is worth skipping.
You may even have some “junk” in your home that could be worth a lot to the right buyer.
Even if it’s not something that you will want to do as a complete career, it can make quite a lucrative hobby.