I ate there last week. We were the only ones there. We sat eating, drinking and chatting for a couple of hours, and the owner was friendly and cheerful enough. We asked how business was, and he replied that he gets enough to get by but is never going to be rich. Consider yourself if you had a taverna with a marvellous view that you kept open all day, but got few tables taken in an afternoon. You'd be welcoming when visitors came, but possibly not very cheerful.
Having said that, I've been to Plakias several times, but only been to To Kastro twice, and never in the evening, so I don't know how busy it is at night.
Arnaki