Read through 6 pages looking for something close to what I would say, and didn't find it. If it appears after p. 6 and before my post, I apologize to OP and any poster that already covered this ground.
But I'm looking at question as "basis for trust" rather than focus on Muhammad. So, like any good debate thread on RF, I'd like that spelled out first.
I hear people routinely say "trust is earned." I get that, but I definitely dispute it. I see it as routinely given, freely. Very much in a cherry picked fashion. You can have immense special (earthly) love for another person and still cherry pick some of what they say (or do) and think they are at times not reliable with their own truth. Still love them, still have general trust in them, but not complete trust.
To me, the obvious basis is your own self. Or what others have said as whether or not the prophecy/message works for you.
Like if someone tells me (circa 1985) that by 2012 the U.S. will be under coast floods due to climate change, that strikes me as prophetic type stuff. I think they'll even believe scientific data backs their assertion up, trying to give it weighted authority. If that same person is part of a group that seeks to have huge hand in politics going forward, then come 2012, they better hope they are right, or it would make sense to lose trust in their ability to predict things. Seeing that I'm referencing something that's political and has essentially occurred, I'm a bit off topic, but kinda makes sense to me to add this to the topic of 'prophecy' and 'basis of trust.' More to the point though is the original message and how it relates specifically to me and what I take to be us/society. Even today, it is presented as 'you need to do more or be willing to do things differently.' I already trust that aspect of the message, but because of what is not being done by own people who believe this tripe (i.e. liberal POTUS uses Air Force One as if jet fuel has no impact on climate), then it strikes me as a message that isn't what I originally thought it was and isn't really about individual me. So, like most messages about 'what's to come' I think I would be wise to learn a bit more about why they might be conveying this. If mostly for political advantage of some sort, I'm taking that differently than spiritual messaging.
But however all that plays out, I don't think I can emphasize enough that trust is foremost always about own self. Then about own self in relation to the messenger or others. Then a little bit about the messenger, unless it deals with politics (foremost). Then I see all that in reverse, where it is less about trust in own self, then about self in relation to the messenger or others, then mostly about what does this group really want (politically) as a result of campaigning for this message. Chances are good they want a grant or ongoing funding related to whatever their message is about.
With spiritual stuff, if it is about what more needs to be done in this world, and that needs to start somewhere besides own self, I take it with a grain of salt. Likely barely relates to me, and to the degree it does, I'm probably already covered or willing to dispute it for what I see as highly misguided rationale.
Will just add that I do realize this thread is about Muhammad more than trust. Unless OP wishes to argue otherwise, I don't think it really is about trust or basis for trusting. If it is, I believe I've been clear in my response to that.