What do we end up with? We end up with the four great problems of Metaphysics. One, that metaphysical content - the concept of thing-in-itself - has no argument or evidence going for it. We have no way of measuring 'reliability' within metaphysics, or what that would mean. Within the empirical world, science is the most reliable tool for measurement. Reliable simply means that it (often) makes accurate predictions. However, the empirical world is a construct of predictions, so even the world 'reliable' CAN NOT be used in reference to metaphysics. We'll get to that later.
The term reliability is an analogue term with a range of values. The term reality is a digital term; it is or it is not.
Metaphysics of reality does not need a guide for reliability, only a guide for reality.
The thing-in-itself is one way, not the only way, of talking about the reality of the thing as opposed to the apearance of the thing.
The second great problem of metaphysics is the problem of the possibility of Metaphysics. It is conceivable (leaving alone possible) that we have evidence and arguments that metaphysics is possible, but that we simply have none for specific content. Meaning that there is something ineffable that we ineptly express with 'existence' when used metaphysically, but that it still denotes something. For this, no evidence or argument has ever been posited. No philosopher hitherto has seen fit to explore this issue.
The statement that reality must be ‘something’ would be an error, if reality were the source of all things including space and time, it may be beyond the very possibility of being a ‘thing’ which is only a concept defined in terms of other things or thing and not-thing.
To say "No philosopher hitherto has seen fit to explore this issue." is simply an error. Huge sections of some philosophies are dedicated to this very topic.
Third, there are very great doubts whether it is possible to mount an argument or evidence for either of the above problems. This means, the third great problem of metaphysics is that there is no reason to believe that we are able to ever do metaphysics. This means, put simply, that there is no basis on which to assume that either arguments or evidence, respectively, ratio or senses, are capable of providing the sort of information that would qualify as evidence of the possibility of metaphysics. Quite clearly, metaphysical content is not empirical, and we have no evidence or argument to believe that our minds are capable of anything beyond rudimentary problem solving.
Metaphysical content need not be empirical, although it may draw from empirical evidence its enquiry is not limited to empirical. However, this does not suggest the metaphysics is in error, it simply shows it is not empirical. As SoS has agreed, we don’t know that empirical is the only way of knowing. In fact we do know that it is not the only way of knowing, therefore to say metaphysics is not emperical does not mean metaphysics is not a way of knowing.
Fourth is a problem of linguistics. Earlier the observation was made that 'reliable' is a concept rooted in empiricism. There's no reason to believe that in metaphysics, concepts/words from empiricism will still work. Take, per example, the term 'causality'. Within empiricism, it denotes a relationship between two events. Namely, that the occurrence of one event necessitates the other. If event A, then event B. There's no reason to believe that this idea applies to metaphysics. The idea that 'the empirical world must be caused', per example, is assuming that causality applies outside of the empirical world. There is no argument or evidence for this. Put short, it is assumed that a domain-specific concept can be used as domain-general. Again, sans evidence, and sans argument.
Linguistics issues are simply that; issues of the limitations of language. This does not mean metaphysics is limited because some every day concepts may not be metaphysically valid.
As per example, 'the emperical world must be caused' is not a correct statement, cause and effect simply do not apply 'outside of space-time'. This is not an argument against metaphysics, rather an argument for metaphysics; the need to understand what can be understood about 'outside space and time' - obviously, any attempt to work mentally on the subject 'outside space and time' can not be limited to emperical measurements within space and time. It is therefore only an argument against using language wrongly, since 'outside' is a spacial term it can not be used to correctly describe 'outside space and time'. This can only be done through metaphysics.
An advanced intellect can consider fairly the merits of an idea when the idea is not its own.
An advanced personality considers the ego to be an ugly thing, and none more so that its own.
An advanced mind grows satiated with experience and starts to wonder 'why?'