I believe most mediums are dishonest and know they can't contact "another realm". There are a few who probably believe they can so aren't being dishonest, but they still can't.
I am prepared to believe that there could be another realm. It can't be proved either way, but I'm not so arrogant in my belief in humanity to think that our scientific knowledge is complete and accurate. Most scientists don't even believe that.
If you accept that something may exist in the absence of proof, you have to accept that there could be one or many parallel universes out there, or an afterlife. That's not the same as believing there is, just that it's a theory that isn't proved or completely disproved at this point in time.
It's like believing there is intelligent alien life elsewhere in the universe. There probably is, but as yet there is no proof. Until there is concrete proof, nobody can say. The universe is so big that I find it highly likely there is life out there. The fact we haven't found it yet doesn't mean much, given that humans have only existed for a few hundred thousand years, have only left drawings and written records for a much shorter period. If aliens visited us 100,000 years ago and left no evidence, we wouldn't know about it today. The same with radio messages and so on, we've only been broadcasting and receiving messages in a relatively limited form for the last 150 years or less. Given the huge distances of space, it's likely that no terrestrial broadcast will have reached another civilization. Even if it had, that civilization would have to be advanced enough to receive (and translate), and to respond to it. Put another way, any radio broadcasts directed at Earth have only had the potential to be understandable if they arrived in the last century or so. Out of all human history that is no time at all.
What I won't do is pay much attention to people who make claims about an afterlife (or alien life) with no firm evidence. Some may be right, but there are so many contradictions, they probably aren't all right.