Whether your a veteran ghost hunter or just learning the ropes there are many things you need to consider when determining a location to be haunted. Not all haunting's are alike. There are a wide range of indications that you must consider in your evaluation. Such as windows and doors slamming shut repeatedly, unexplainable sounds, and unknown odors. These are all legitimate signs of the phenomena. Some haunting's feature a single phenomena, such as objects moving on their own. While other haunting's offer the feeling of being touched or hearing disembodied voices. In some very rare cases you might even run into a full bodied apparition.
Here's a list that covers most indications that your location maybe haunted:
A general uneasy feeling: like you are not alone, or the feeling of being watched are common in most reports of a haunting
The feeling of being touched: some investigators report that either their hair or an article of their clothing has been tugged on or something touched them, usually on their arm, hand or leg
Unexplainable movement: such as a shadow or light, the more extreme is to witness an object move on its own. For example chairs, tables, books, etc... The most common report is of something walking by them when no one else was there.
Strange pet behavior: A dog growling or repeatedly barking at something you are unable to see, or sudden refusal to enter a particular room or area of the location when in the past there was never a problem. You may even see the dog dart or dash as if something is chasing it away. Cats are another good indicator. They will occasionally sit there and their heads will move as if they are watching something invisible walking across the room, and sometimes they may get up and follow whatever is there. Cats personality are different from dogs, they are more likely to stick with a possible entity rather than run away. Animals also have sharper senses than humans, and many paranormal researchers believe their psychic maybe more finely tuned as well.
Electrical and appliance issues: Reports of TVs, stereos, lights and other electrically powered items, turning either on or off when the witness knows it was left the opposite way.
Unexplained Noises: such as foot steps, knocks, banging, and scratching sounds. Sounds of something being dropped or shuffled. The sound of doors and windows opening or closing. Sometimes these noises can be subtle or extremely loud.
Items disappearing and reappearing: Personal or commonly used items, such as car keys, hair brushes or cell phone, that suddenly disappear. Most people search high and low for a missing item but have no success. In some cases the items will go missing for days or even weeks, only finally to be found placed back in its original location. Some paranormal investigators call this "the borrowers" phenomenon.
Unexplained shadows: The sighting of unusual shapes or shadows moving at a fast rate, usually seen out of the corner of the eye. At times these shadows resemble a human form, with a dark gray or black color. Most people who witness this say, they see a flash moving in various directions.
Disembodied voices and whispers: a phenomena where a witness says they heard a voice saying something to them when no one is around, or multiple witnesses hearing the same thing with no explanation for it. Not only does this come in the form of voices but occasionally people will hear music coming from nowhere. Also a disembodied voice is heard with the naked ear, where as something such as an E.V.P. is only heard after playing back a recording device.
Unexplained temperature changes: These are also know as "cold spots". Usually a fluctuation of 10-20 degrees in a localized area indicates some either tryed or did manifest itself. Cold Spots are a classic symptom of a haunting.
Unexplained smells: the appearance of smells in the home, usually that of unfamiliar perfumes or colognes, that the witnesses do not recognize. This usually accompanies more severe phenomena such as full bodied apparitions. Odors such as rotten eggs are also reported.
Apparitions: the appearance of a physically visible phenomena, such as a mist or shade all the way to a being that looks solid and alive until it disappearing into a room or walks through an object it shouldn't be able to. These types of phenomena are very rare and if encountered should be documented as thoroughly as possible.
Physical Assault: hard shoves, slaps, and scratches are extremely rare, but if encountered leave the premises immediately.
Above are the most commonly reported occurrences of people who believe their residence to be haunted. We are not saying that all of the above will occur, and its possible that some things we did not mention could happen as well. It can get far worse, or there maybe a simple natural reason for what you or the client maybe experiencing. Odd noises don't have to be a spirit, it may just be a house settling, bad pluming, or possibly a wild animal. Check for problems with the structure, such as holes in the foundation, you may find a family of some creatures living inside the internal structure that can wreak all sorts of havoc. The same applies for investigating a business, if the property owner is complaining about windows and doors opening and closing, it could just be rusty hinges or a strong draft if the structure isn't properly insulated. This can explain away cold spots as well. At the end of the day, the majority of occurrences have a reasonable explanation, so before you tell a client they're haunted make sure you have the evidence to back it up.