Hi, this is a bit of a late reply as i'm not on the forums much. I am working the Quareia course and of course have read and worked the trilogy book. The first thing to appreciate is that our society has labelled 'imagination' as unreal fantasy, and magic takes the completely opposite view, that imagination is in fact the tool used to create and connect with the void and the inner worlds around us.
So the first thing to consider is that your imagination is actually the tool you use in magic to connect to the inner worlds and contacts.
Skill with vision work generally takes time to develop, just like meditation itself. With meditation, initially you have the babble of your mind to pass through before you deepen into silence. Once you have reached a state of silence, then visions will begin to appear which are not generated by your internal dialogue or superficial mind - they are in fact communication from the inner worlds, which you can choose to accept or set aside.
so there is a level to pass through before you reach genuine contacts.
Visionairy work is something similar. With inner silence, when you reach out for contacts from a certain level, genuine contacts have a certain quality to them that becomes familiar. Much of Quareia is based around natual magic, and the associated visionary work will produce actual effects or changes either in yourself or the world around - eg when a contact reveals something to you, then there will be a corresponding change in the reality around you. I often experience delayed effects, eg something will change in my life following a ritual. Eg when i was contacting the 3 fates in ritual, and working with Atropos - who cuts the cord of fate - the very next day a major ending came in my life which was rather shocking and unforseen. A common occurence also are sudden weather changes around me when i am doing ritual outside.
So how do you know that it is real? Because the visions you experience will link to actual events around you. This takes a little practice.