Recent work has studied the impact caused by attackers that compromise pricing signals used in the emerging retail electricity market and send false prices to a subset of consumers. In this paper, we extend previous work by considering a more realistic adversary model that is not arbitrarily tied to scaling and delay attacks, but that can generate any arbitrary pricing signal and show how to keep the problem tractable with a new analysis based on sensitivity functions. In addition, we extend previous work by proposing countermeasures to mitigate the negative impact of these attacks. Countermeasures include selecting parameters of the controller, designing robust control algorithms, and by detecting anomalies in the behavior of the system.