If the cover is rubbish like a lot are for self-published books, I will go right past. Covers that look to my like someone is trying to do fantasy but really it's romance, I will go right past. Most books that have a bare chested man on the cover is romance and I'll go right past. The cover has to catch my eye unless it's a book I am looking for or an author I know of.
Have a look at this sight for some pretty lousy/funny covers.
https://lousybookcovers.com