I personally never recommend an exorcism. I will tell you why.
If you have a nice friendly ghost on your hands, you should leave it alone. If you try to exorcism it I guarantee you will now have an anger ghost on you hands. It will refuse to leave. You have to think about how you would feel if your human dwellers where trying to get rid of you and you are just a nice friendly ghost who wants to share their space.
When you do an exorcism again you are opening up a window to the Spirit World as well as the Dark Realm where evil dwells.
You may exchange one angry ghost for another more angry ghost.
Most ghost are friendly. They are harmless and should be able to stay with you, they are also good protection if evil should try to knock on your door.
If you feel that an exorcism is your only alternative, I recommend you get a professional who will come out to your house and do it.
If not you better make sure you know what you are doing. Get the help of other Wiccans to assist you. I do not feel that most would agree with an exorcism, they could come up with things you may not have tried yet.
Same goes for Banishing Spells. You are again opening up the window to the Spirit World as well as the Dark Realm.
Always be careful. Learn more about these things. Ask other Wiccans. Remember that's why my club is there to help anyone who needs it. If you have any questions please feel free to contact me or my club.
Please be careful of anyone giving out detailed instructions on doing Ghost Hunts or Exorcisms. Or anything else that doesn't feel right. These are things you should not embark on alone or do if you are inexperienced. Ask some one else for their opinion before you try. Someone experienced that you trust.