Rabbi, there are many stories in the Gemara and later about certain people meeting Eliyahu HaNavi, how could one prove that this actually happened, especially when it adds a lot to Judaism and the like, for example Arizal. Even then, on an individual level, how would one know if he met Eliyahu HaNavi personally, and what would differ between this meeting and Eliyahu HaNavi coming before Moshiach (may he come quickly in our days)?

This topic is pretty esoteric, and the concept of "Giluy Eliahu" is some form of Ruach HaKodesh, or low form of prophecy. The Rambam writes that prophecy is 100% clear and unquestionable that one is speaking to God, on the other hand, this is not written about lower forms of Divine help or inspiration. Only those who have had a "meeting with Eliyahu" could explain exactly what that means. In the process of Torah study, sometimes one receives, all of a sudden, a "brainstorm" or chiddush "out of nowhere", which is sometimes called Ruach HaKodesh. All this as opposed to Eliyahu HaNavi who will accompany the Mashiach, who literally is a person who, according to tradition never died. By the way, I think the average person can sometimes actually see Hashem Himself in His Divine way of running the world, which for us, is a lot more important, beneficial and even more understandable than the topic of Eliyahu appearing to other people.