The ones tied to a real shopper worry: secure payment handling, a clear returns promise, and a reachable support contact. Generic badge walls with logos shoppers do not recognize add clutter without adding confidence.
Yes. Overloaded checkout headers look defensive and slow the page. A small number of specific, verifiable signals near the payment step outperform a collage of seals spread across every step.
Close to the moment of doubt: beside the payment fields for security, near the total for price and returns reassurance. A signal on the homepage does no work for a hesitation that happens at payment.