For me the cover often indicates a subgenre I might want or not want to read. Half-naked male torsos on the covers of romance novels turn me instantly off and I won't buy it (I do read romances occasionally). A cover indicating a cozy novel or a harem/men's adventure novel usually makes me scroll on, although there have been a few exceptions. A generic mystery (yes, these silhouettes
)/fantasy/SF cover and I usually read the synopsis.
As to the quality of the cover, I don't much care unless it's egregiously bad (in my opinion, of course). I do read the synopsis sometimes even then.