Question

“Clearly roses are the best flowers for gift giving, because I see more people buying them than any other kind of flower” is an example of

Answer 1

It is an example of bandwagoning.
Bandwagoning is a phenomenon in which people do something primarily because other people do them; in the process they go against their own beliefs by overriding or ignoring them. Bandwagoning is especially seen in consumers behavior and in politics.