The main disadvantage of e-PR is that it is not a controlled discipline like online advertising techniques such as pay-per-click marketing or display advertising where the returns generated will be know for a given expenditure. In other words, it could be considered a high risk investment.
Many marketers are also wary of creating blogs or forums on their sites which may solicit negative comments. However, there are counter-arguments to this, namely that it is best to control and be involved with conversations about a brand on the site rather than when it is less controlled on third-party sites. For example, brands such as Dell and Honda enable web users to make comments about their brands so this shows they are listening to customer comments and gain valuable sentiment that can feed intro new product development ideas.
Chaffey, D. and Ellis-Chadwick, F., 2012. Digital marketing: strategy, implementation and practice (Vol. 5). Harlow: Pearson.