Can't find the study, but it was statistical analysis of results of different wine competition. The result was something that bad wines was always viewed as bad, but on the good part of spectrum the good wines ranked kind of randomly.

So it is more like we know what we do not like, but there is very little agreement on what is considered to be good wine.

You can't obviously. But when it comes to wines there are certain flavour characteristics that are desirable for that particular type of wine. So a 'good' wine is a wine that shows more of those characteristics and a 'bad' wine is a wine that has less of those characteristics and more 'undesirable' characteristics. Whether or not you think those characteristics taste good or not is a separate discussion.