complicated topic for sure.
we have adsense ads on the site because we want to offer the visitor more related resources, it's not really for the ppc revenue.... it does help pay for some site expenses though.
The ads are in the same market sector and peeps like bestblanks, spreadshirt and others also do not have a problem advertising on the site.
We do get sales from our sites adsense advertisers too, when they can not fill the users needs they often refer them to us. OR we fill orders for them and they sell it to their clients.
I think this type of B2B referals stuff goes beyond adsense and it is done a lot within all industries i find. The ones that don't are usually not what they proclaim to be or are not confident with what they sell.
like i said, this is a very complicated topic and i bet there is no perfect answer.
