Many times people have described their experiences of seeing a ghost to me. Then they often go on to doubt what they saw and try to find a rational explanation for it. That's fine, we should always question our experiences and try to find a scientific reason for any phenomena before coming to the conclusion that something is a paranormal event.
There is one way to tell if you are seeing or feeling a spirit or ghost and it's something we can all do and naturally have available to us.
The trick is this - if you experience an emotion at the same time as sensing or seeing something external to yourself then the chances are that it's a spirit. Spirit people are the sum of their emotions - they no longer have a voice or body to express themselves with. They use our nervous system in a very subtle way in order to communicate with us. Our aura also registers the energy of another being and can pick up information that with practise we can learn to interpret and understand.
We have a habit of brushing aside our emotions when they catch us unawares but next time it happens to you try to hang on to the feeling long enough to work out if the emotion truly belongs to you or if it is being projected to you for the purpose of communication. There is no need to hunt for these experiences - they are everywhere - even in your own home at times. Be open to new sensations, be aware of your sense of self and how your emotions work and you will be able to sense outwardly more easily.