Hi there,
It's hard to say categorically the dos and don'ts, especially if Sedo closed your account without reason - which, as far as I know, only happens in cases where they are absolutely sure that traffic has been generated / clicks have been incentivised.
Basically, the people on a parked site have to want to be on that domain without being pushed there, told to go there etc. This essentially limits parking traffic to type-in and existing search engine traffic. We certainly don't encourage advertising parking pages, buying traffiic, redirecting traffic etc as this generally converts poorly and Google get grumpy.
Parking domains is not really about generating huge swabs of cash from unsuspecting visitors to your domains but about monetizing inherant traffic on your domains to the best of your or your parking site's ability.
If you have any direct questions about what is and what isn't allowed, then email or PM me and I can clear it up for you.
The bottom line is: Real people genuinely looking to be on that domain (or with a typo - thereabouts) who are actually interested in the advertising on offer.
Ed