Keep your costs down. In order to turn a profit on what you're selling, choose to sell an item that's inexpensive to make. Lemonade is a classic because all of its ingredients (water, sugar, lemons or lemon juice concentrate, and ice) are fairly cheap and easy to obtain. Popsicles are another favorite because they can be bought in large quantities from the store!
What’s the catch? None, really. Cash back apps act as affiliates for many online merchants, which means that whenever you make a purchase through one of the apps, they get a small commission — but then, they give you a portion of that commission as “cash back”. For example, if I buy a pair of Nike shoes through the Ebates app (or website) and spend $75, Ebates may get a $10 commission but then they’ll pass $7 back to me. It’s basically a way to get sale prices on stuff that isn’t on sale!