Here's a hack. Use the referral header or url tracking parameters to redirect the URL to some place seedy or maybe their competitor. I'm sure they'll change it quick after that.
Will stop people from contacting them in favour of real businesses if that's the case.
It's 100% within his rights as the website owner, and it will highly encourage those who can change this to do so.
I love it.
I respect the opinion though, so not down-voting you.
<script>
window.history.back();
</script>Preferably one that won't hurt a young kid that accidentally clicks on it I presume?
That business can potentially claim damages.