It is argued that there is more counter arguing if the message is one-sided instead of two sided. (A message is one-sided if it presents only positive arguments or attributes and two-sided if a few qualifications, usually about relatively minor attributes, are presented.) Two-sided ads are seen as more credible, because they admit that the advertised brands have some shortcomings.
However, not all two-sided ads beat one-sided ads in credibility: research has shown that two-sided ads are especially credible when the attribute on which the weakness is admitted is
(a) Relatively unimportant, but not trivial, to consumers;
(b) Perceived to be negatively correlated with the attribute on which superiority is claimed (e.g., “we are more expensive (weakness), but only because we give you higher quality”);
(c) One that would not otherwise be known to consumer’s prior to purchase, so that the advertiser gains some “brownie points” for honesty.
Other research has also shown the general superiority of two-sided appeals, especially with more educated audiences, and with those consumers initially opposed to the brand making the claims, and on attitudes rather than purchase intentions. These results suggest that comparative ads are more likely to be persuasive in changing brand attitudes if they are two-sided rather than one-sided.