Romney is running on a conservative platform. Conservatives who are trusted, and who have a lot to lose if they get it wrong, have spoken with Romney and said he is telling the truth.
Romney's speeches, campaign platform, debate answers, interviews, all espouse conservative principles and show a man who believes what he is saying and means to do what he claims.
It’s Romney or Hell-On-Wheels.
I don't know who these trusted conservatives are, nor do I doubt your characterization of them. But I do doubt that they have a special ability to detect deception simply because they are known and trusted.
My sense of Romney (who I respected enormously at the start of the campaign) is that his positions are not particularly sincere, but rather market-tested. Every one seems tailor-made to what conservatives want to hear, regardless of what he has said previously. (The exception is his supposed support for keeping the Dept of Education, which would never be a dealbreaker).
This phoniness would doom his candidacy in the general election.