If you see someone is getting rid of a lawn mower because they don't know what is wrong with it or just because they don't want to pay to fix it themselves, pick it up even if you don't need a mower. Flipping small machines is a great way to make some extra money, and you can scope out the classifieds for more mowers that are being given away or sold at a low price because there is something wrong. You can then take the machines in at the same time. Do the following.
Find a Local Repair Center
A center that does lawn mower repair can diagnose the problem with the mower quickly. You can then decide if you want to fix it and keep it or sell it. If you decide that you want to fix it and sell it, make sure that you get it a tune-up while you have the machine at the repair shop. That way you know it will run great when you're ready to sell it.
List the machine for sale on local classified sites, through social media, and even by putting it in your front yard with a sign on it. If you can at least double the money that you put into the machine to originally buy it and then repair it, then it was worth the time to repair it and flip it. You may even want to say that you are open to the highest bidder.
Take Antiques to Trade Shows
If you find a very old lawn mower that someone is getting rid of, it may be an antique and it could be highly valuable. There are many antique dealers and classic collectors that want these old items for the own collections and to sell at large trade and antique shows.
If you end up fixing the machine and you can't find someone that wants to buy it right away and you want cash, you can try to take it to a scrap yard. If the cost is too high at the lawn mower repair service shop to do the necessary repairs to get it up and running, this is another time when you may decide you want to take it to the scrap yard and sell it for the metal. Find out the best solution and turn a profit scooping up the mower, fixing it, and selling it.