It might be worth creating a thread (sticky) with a disclaimer, rules and guidelines.
So you cover your back, while stating that the machine or software that the end user purchased, was not purchased in a legal manner, as in not from you.
No support will be given on software brought from third parties, however the forum is still open to them to problem solve.
Advice that due to other people being on version 9 or later, no backwards support can be given, as bug fixes have improved the later versions.
Just general stuff like this, and worth while updating your software (maybe at a very small discount)
Regards
Mark