Well technically I ask that whatever is being sold relates to Z-cars in some way or at least Datsun's. Or it should be of interest to our members in some way shape or form. The rule is slightly more flexible for long term members / posters.
We obviously don't want our classifieds overrun with Commodore's or Volvo's.
Remember they are free and if we find that all of a sudden we need to spend lots of time administrating / moderating them, we may need to start charging for them.
If you are selling something not related to Z's, perhaps the best place is the Off Topic section of the site?
A good rule of thumb is, if in doubt contact us first and we will give you the ok. I usually mention that you should write a note saying you have permission from Admins to post this article.
Otherwise sometimes the Lurch monster deletes things, but remember he's only doing his job

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