Welcome to steem! )
Reading the comments it sounds like you're familiar with Australian regions. As I live in Australia, I don't mind Shiraz. Maybe you have some inside knowledge as to the reason why large wine retailers such as Dan Murphy, BWS and 1st Choice have so many undrinkable wines even well over $15. I suspect similar experiences occur in places like the US and UK too.

Is it a case of wineries dumping their below standard product on these retailers whilst the better ones are exported or sent to premium shops? Buying wine from these places is a lottery, occasionally you find something decent, but after a lot of money is wasted on duds :). I know there are better places to buy wine, but they're not always conveniently located. Maybe this is a blog post idea (for you) I'm working up to here, but any advice as to how to more easily locate the decent wines among sea of awful stuff in these places and save some money?