The sciences can be wrong, can falter, can yield what appear to be facts but which are not, and so on. However, perhaps its defining characteristic is the degree of objectivity it offers against personal epistemologies.
I think that's what science used to believe was true, but is more and more realizing that it gets in there too despite the checks and balances. Isn't this true?
Mysticism is not necessarily some subjective free-for-all. Just like science, you have those who are students, learning the discipline and those who are experienced masters. Just because a student may differ widely with another student in how they interpret the data, does not mean that science is unreliable, does it? So too with mysticism.
And then outside of science you have the public viewing the scientists as telling them facts of the "real world", and create a system of philosophical and religious beliefs surrounding how they hear what the scientist say, inserting their own personalities, hopes, desires, etc., into a belief system about this "reliable source of authority". Scientists who are themselves not young idealists who think they are on some perfected path to knowing absolute truth, will shake their heads at the public who starts religions in their name, realizing they're putting way more faith into their work then they themselves do, to the point of proclaiming dogmatic truth. This is no different than with the mystical disciplines, with its Masters, students of various levels of expertise, and the mass public looking to them for Answers, with a capital A.
Note I am using the word discipline here? It's not just making stuff up, rather it follows a pattern of actual first-hand data collection, experimentation. As godnotgod metaphorically put it at one point you have to "look through the telescope". This is true, you have enter within contemplative space through the eye of contemplation, not just sitting there speculating in philosophical thought what might be up there in the night sky without following any sort of injunction or actual data collection.
Next you have to actually collect data to examine. Not all experiments yield results, of course. You may have clear obstacles that inhibit seeing the data, such as moving the telescope above the atmosphere where the water molecules are causing interference with its ability to see into space. In the case of meditation, the eye of contemplation where one peers into the deep-field of inner space, you have to get rid debris which obstructs clarity, which is noise interference; in the many and varied forms of chattering mind, blockage due to inherted models of reality through culture and language (which interfere in science itself as well, mind you), etc. It may take years of specialized work to tune the tool, like fixing the lens on the Hubble telescope. Additionally, the person doing the research has to be trained if they hope to be able to talk intelligently about what is seen once they look into the deep interior spaces. (Science is about exterior spaces, contemplation the interior).
And then, when the qualified researcher uses the proper tool which has been adequately calibrated, collects the data, he then attempts to describe his finding and propose models to look at that data with among those who are his peers in his field. Those models of course, are not the reality of the data itself, but a way to attempt to talk about it. Those models can and do change, or even in some cases are utterly abandoned if sufficient data comes along that doesn't fit that model any longer. Some models, such as the Theory of Evolution are so well attested to from so many angles, to unseat it as a standing theory is unlikely.
This is no different than the mystical discipline. How does someone test the mystical apprehension? Do the experiment. Learn how to do the research, and do it. Learn the ways to model it and see if your own research corroborates or challenges the models. Young idealist students may speculate beyond themselves as to what the findings suggest, as is true in any discipline, but this does not mean the data they are looking at is bogus, by any means. And just like the empirical sciences, those who are Masters caution students in their zeal to make sweeping pronouncements about the data in applied areas. "I've seen God. Science is therefore crap!" No, of course not.
Then of course you have the general masses may view them as the Answers gods who start movements and religions and ensue in religious wars in their names, the Dawkinites go to war with the young Swaminites, and so forth, never even actually practicing the empirical science themselves, or the science of contemplation. They are in some cases hacks, in other cases just "True Believers", clueless to the reality behind the religious masks they supply to the questions.