TripAdvisor unveiled a new partnership that is expected to add more credibility to some of the 100 million reviews of hotels, restaurants, and stores on its site. American Express members can now link their cards to their TripAdvisor profile, and any review of a service they buy with their card will be designated as an ‘‘Amex Card Member Review.’’ This will give users of the Newton-based travel site another way to verify that the descriptions they are reading are real.