So, you just don't want people to be able to host other domains on their account (i.e. no add-on domains)? I'd just turn them off and not worry a terrible lot about it personally. People are more likely to find a provider that will simply give them an account with add-on domains than to go out of their way to manipulate your account limits.
Addon domains are fine and parked domains are fine too.
What I am talking about is that if I let them park 10 domains just for SEO purposes that should point on their main site's URL, then they should not be able to redirect the parked domain's URL to another dir.
If they are able, then it is almost like an addon domain, which they surely would need to pay for if I let them put an addon domain to their account.
For parked domains they might not need to pay, because why not have more entries to the same site.
I hope it's clear now what I would like :-) Am I thinking something wrong?
All I would need is to disable .htaccess for parked domains, or perhaps create automatically a 301 redirect to the main site, so the people could do nothing extra with it. The redirect would be the best.
I have a bad experience about parking a domain for domain mapping/creating network sites. Something happened with the sites and when we contact our host' support, he said that it's because of the changes made on .htaccess. That;s the reason why we no longer do parking of domains but addon domains work great.