Do you think a psychic is a psychic, is a psychic? Ouch. You cannot cut psychics from a cookie-cutter and you cannot assume that all psychics know the same things or have the same abilities. You cannot throw a blanket over psychics anymore than you can spells. Psychics are individual and each psychic, like a person, has their own strengths & weaknesses.
If you have two psychic readings from two different psychics and they don't provide you the same information there is a good reason; they see you in their individual ways. Some psychics are more in tune with seeing love issues, some see family situations, some see a bigger picture in general without specifics. There are never going to be two psychics who see exactly the same thing because they are each unique. To put it in perspective for you it would be the same if you approached two artists and said to them both "I want you to make me a statue that you think I'd like", without either artist knowing you personally and with just their initial impression of you to go on they are both going to return with different statues. It doesn't mean that one artist is necessarily better than another it means that they each saw something different in you.
Should you use one psychic to validate another psychic? No. Just as explained above no two psychics are going to share the same abilities. If one psychic tells you that they see marriage in your near future and you want a second opinion I would start by choosing a psychic who has love sight specifically and then procee by telling them "I'm interested in what you see in my life in regards to marriage". I would then take what both psychics told you as a guideline.
Are what psychics tell me always 100% accurate? Yes and no. When they read for you they are taking a look into your life as it stands at that moment in time. Psychic readings should never be taken as direction on how to live your life; it should be taken as guidelines, signifiers on approach to life. Your future can change based on the decisions you make each day so certains things seen in your future on Monday could be different by Friday. This is why it is important to take psychic readings as a guideline to watch for certain things should they come to fruition and if they shouldn't then your path has changed since the reading.
Working with psychics is very much like working with spells & magic from different cultures; they should be understood for their differences and applied accordingly. Some psychics are born with their sight, some develop it at different points in their lifetime naturally, some work to develop psychic skill and some use tools of divination rather than being the tool themselves. From their each psychic stems into branches of ideology, religions, working on different realms, and so many other factors that it is easily recognized that each psychic is unique.
If you are interested in working with psychics you have to approach them with this perspective and understand you will receive individual results.