Answer to Question 1
Researchers should maintain both anonymity (who has participated) and confidentiality (not letting others know how they responded) when possible. For research that follows people across time, it may not be possible to guarantee anonymity.
One problem with discussing anonymity and confidentiality with potential respondents is that if the researcher stresses it too much, respondents may become suspicious and either decline to participate or alter their responses.
Answer to Question 2
a. journals are reluctant to publish exact replication because new knowledge is seen as better than old
b. researchers themselves are reluctant to submit a replication because they don't believe that journals will take it seriously
c. most researchers generate studies with some novelty, so other researchers do not want merely to replicate
d. funding for research may be limited because funding agencies want to support novel research
e. previous research reports may not provide enough detail to allow subsequent replication