Backstory: While playing poker tonight a friend brought up how his wife purchases random items on Amazon and he feels they don't need it. A few other friends have brought up a similar issue with their significant other.
The Idea: Before the Amazon purchase can be fulfilled, both you and your partner must agree to purchase it. Kind of a sign off from both parties and it helps each other know what they're buying.
Deep Dive: You could turn this into a discussion where you could offer an alternative product or prevent your partner from buying something poorly rated.
Validation: A few friends have already asked for this and it would be a great way to help merge finances in early marriage situations.
Monetization: You could offer similar items through amazon or other channels through an affiliate link. This is a small niche app that is designed to help save you money, it's hard to charge a monthly fee.