I figured I'd post a response here instead or replying to your PM so others can chime in (or learn).
You could have two sites. Site A would be the adult site and site B is the "white hat" site or better put, the legit looking site. Site A might have a membership for porn and direct the user to site B to buy the "Website evaluation service" on site B. Site B would sell generic "Website evaluation services" and mention nothing of site A. PayPal would never know what you were doing. All they would see is "Website evaluation service" sold and think nothing more than a site selling their services, totally legal as far as they're concerned.
Just make sure the "whois" does not show both sites (A and B) as the owner. If someone tried to do a chargeback and show paypal site B and where it states that you have to buy the "Website evaluation services" to gain access, you can rebutt that by saying that you don't own site B and have no idea why that website is sending visitors to your website to purchase. You then thank them for bringing that to your attention so you can investigate and demand they not link to your site anymore.
I would send a generic "Thank you for your business, everything checks out okay." email to each member that pays you. The reason for this is if they complain to paypal to try and charge back, you can show PayPal the email you sent them from Site B (the good site) that reads "Thank you for your business, everything checks out okay.", which proves that you performed a service, possibly checking their website to make sure they've optimized it correctly for search engines perhaps.
Hope this helps.