The old "don't judge a book by its cover" adage has never made much
sense to me. You can tell a lot about a
book like this one by looking at the cover. I mean, any idiot
could see that it's a field guide
for picking wild mushrooms which was written by an impishly deranged
trombone enthusiast named David who enjoys feigning the thievery of
large quantities of fungi while wearing a cheap 80s tuxedo.
As such, I'd say that the cover is a valuable resource for buyers, as
they know precisely what they're getting when they purchase this book.
And sure enough, if you read the reviews, you definitely don't see any
customers complaining that they "feel totally mislead due to the fact
that they bought this book expecting a dry treatise on spearfishing
penned by an elderly black woman on a horse and got a mushroom guide
written by someone who is ostensibly insane instead". So I think
you'll agree that in this particular case, it's more than fair to judge
a book by it's cover.
But as for the actual quality of this book...I can't really
speak to that, as I haven't read it, and don't plan to. I'm not really
whole "deliberately going outside and performing actions" thing, so I
probably wouldn't have given it a fair shake anyway.