No summary or contract is trustworthy, so no, they shouldn't trust it. Trust is between parties, not between papers. It's more of a shortcut and guide. If there's something in the summary that's a red flag, well we just saved a lot of time by finding the matter fast. If not, then we should have a good idea what's in the contract, and if that contract significantly differs from the summary, then the party isn't trustworthy. It's much easier to read a contract with an idea of what it's supposed to say, than going in blind. With the summary, your mind is more focused on "is X true or false" rather than determine what it says, THEN see if the details are kosher.