When persuading Americans do not feel obligated to offer full and comprehensive information about the weaknesses of their proposal, concept, product or solution. Instead, the obligation is with the buyer (the audience) to expose the weaknesses through critical questions. If asked, competent, professional and honest Americans will respond forthrightly.
Are Americans less honest than others? Perhaps. Perhaps not. Who can judge? Not our topic.
This is a shared logic among Americans. Listeners know to ask the critical questions. Speakers know to anticipate those questions. If the critical questions are not asked, if the listener then accepts (buys), only later to discover negative aspects, the listener (buyer) will not blame the speaker (seller), but himself.
Besides, who wants to admit to their colleagues or boss, to their spouse or friends, that they made a poor decision?