It’s a good sign that energy is moving and that it’s beneficial to you.
Whether it’s because Marbas is present is a different question.
Great. I’d call that an “intuition”, it’s usually helpful to follow your intuition. 
We all have that question. No there’s no way - UNTI you get results that Verify your UPG. (UNverified Personal Gnosis).
The vast majority of things cannot be proven upfront, all we have to go on is words and ideas, impressions and subtle interactions with the unseen, and common sense.
It’s more helpful to suggest tools by which people can hone their discrimination (such as this essay, “Magic needs a curious mind”).
Always keep questioning, it’s how you keep it real, and don’t end up a madman who’s just LARPing his way through “magick” in his imagination. Look for verification, which sometimes comes by running with it and finding out if you get results. Results are the entire point for most people.
I disagree with him, or perhaps your interpretation of the impressions he gave you - you don’t need to trust him whatsoever, you have to trust YOURSELF and that what your heard is what was real. If you can trust that, then it’s like a conversation with any other person, you listen and then make up your own mind.
But that’s me: I immediately distrust anyone who feels the need to tell me to trust them. If their words don’t stand on their own merits regardless of who says them, then they are worthless.
Red flag for a parasite here. Marbas can heal and you don’t have to give him anything. You most likely need to work on yourself with his support. Tit-for-tat is not how higher beings operate.
The proof will be obvious - parasites make promised tey can’t keep. If you feed it, and you don’t heal, then it blames you for not doing enough - then you will know you has your time wasted by an impostor.
If you’ve been lurking on this forum for years, they you have probably seen this link here - scroll to the “how to identify impostors and other time wasting things” part, and get a refresher. Not saying he is, but just in case.
What other people think is not your business - I advise against attempting to evangelize for this or any being. State your experiences but let people make up their own minds. Major red flag here.
Red flag #3: Dude! you’re already free and it’s NOT this being’s say-so to say you’re not. YOU are the mage you are human, you are more powerful than it and it wants your milkshake and is trying to get you hooked by letting you think it’s got something you need.
All in all, if you want my opinion, this isn’t Marbas - banish the fuck out of this thing and get it gone for good, it’s a lying , manipulative POS that wants you under control and that means nothing good.
Then go and fix your wards and protection because they aren’t working.