Generous return policies make shopping easy. After all, if you don't like it, you can return it. That could lead to overspending. If you're prone to this type of thinking, establish a personal "no return policy" to keep your spending in check.
Photo by out of ideas
Of course, if your purchase is defective, broken, or doesn't perform properly, return it -- no need to be that strict. The goal is to avoid the "eh, I can always return it" attitude -- especially if you know you probably won't.
You have to be willing to be stuck with an item though before you buy it. This internal policy makes you think hard if you need something now rather than buy-and-return-it-later. Check out the link for other ways stores manipulate our buying behaviour.