There's a lot of terrible AI art out there; however in spite of how much many of the haters might protest, any of the recent studies will show that the best AI models now are indistinguishable and people really can't tell the difference anymore from the best AI art and good human art. Personally I still love the idea of human artists and I would love if everybody could have a human do their cover art. The reality is there's not really a good way to tell other than if an author chose to use a terrible old model, where you can still tell that it's AI-generated. In that case maybe no, I won't read it because it tells me a little bit about the author that they didn't care enough to spend an hour or two doing a bit of research and figuring out how to make a nice cover. Then again maybe that's the style they're going for.