A web site I'm working on sells vehicles to business entities only.
Consequently, it displays data aimed at business customers (prices without Value Added Tax, warranty limitations, etc.). In Germany, showing this kind of data to private end-users can be punished as misleading advertising.
One way around that is to show a dialog when the user enters the site. In the dialog, the user must confirm that they are a business user.
My idea at the moment is to use a flag in $_SESSION to detect whether the user is new, and then to redirect them to a confirmation page using a header redirect. When they confirm they are a business user, they get taken to the actual page.
However, search engines should see the content straight away, without the confirmation page.
Does somebody have a genius simple way of detecting search engine bots
Without the use of JavaScript
Without the need for constant maintenance (e.g. a list of spiders' USER_AGENT strings)
Bot detection doesn't need to be 100% reliable as long as the major search engines are served properly. Any other ideas on how to fulfill the legal requirement of having the user confirm their business status are very welcome as well.
The web site is based on PHP 5 and runs on a Linux-based shared hosting package (can't install any extensions).