Research selling prices of items similar to yours. Look up completed sales or current listings of items similar to yours. Find the high- and low-end prices, and price your object around the median price level. If you want your item to sell quickly, price it at the low end. The condition of the item also affects the price. Items in poorer condition should be priced at the lower end. Also, consider how many listings there already are of items similar to yours. If many similar items will be competing with yours, you may have to set the price lower to get the sale.
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!