Is it possible to continue as a bitcointalk member even without trying too hard to achieve a single merit?
This is what the forum is all about, I've said it many times. Don't chase the merit, just post when you feel you have something to say, not because you are pushed to post by the sig. campaign rules. Then you don't have to worry about the merit, and it will come eventually 
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Does the merit have anything to do with trust ratings?
No, trust is only market-related and you build it only based on your training history. There are some exceptions too, like bad behaviour not moderated by the forum staff sometimes lead to a negative trust from the Default Trust Member (DTs), those are scams, merit abuse, asking for loan without collateral, cheating on bounties with alt accounts, etc
