Too Long; Didn't Read
Only a few methods that claim to enable you to see someone else's Facebook messages actually work. Most of the apps and websites are simply scams trying to get your data by making false claims. The only method that actually works if you are looking to spy on someone's Facebook is spy app. Spy apps work in the background and collect and upload all the information to the cloud, which you can see through a web portal using a browser using your credentials. It offers all the features you want, along with exceptional customer service.