I heard about this years ago, and just looked it up again to see if people were still doing it. You can get lost golf balls out of golf course water traps, and sell them. I wouldn't recommend this if you live in alligator country here in the U.S., or at the Carbrook Golf Club near Brisbane, Australia (just watch the video).
I ran across this idea several years ago, when I was back east, and couldn't find any job. While it wasn't for me, it stuck in my mind. This can work a couple of ways. Either you make a deal with the golf course owner/manager, to either scuba dive, or drag/rake the bottom of the water trap ponds, to recover lost golf balls. You can provide the service for free, and then wash and sort the balls, and sell them on eBay. Or you can do this for a fee paid by the golf course, and give them the balls to resell. Do the needed research, and talk to golf course managers, if this sounds interesting, and see which method might work for you.
Here's a news segment about a golf ball retrieval business in Virginia. There are 3 or 4 kinds of "rakes" to do this from land, from this to this. So scuba diving to pick up the balls is not the only method, though it appears the best method, if you're a qualified diver. Then you can make deal with the golf course, and sell the balls back to local golfers, or on eBay, Craigslist or similar sites.
