First up, not wanting legal advice as I know its not allowed, but maybe someone has previous experience that might help.

A classified listing on TradeMe is considered an Invitation to Treat, is it not? I'm sure this discussion or one similar has come up before but I couldn't find it via a search.

The terms and conditions on TradeMe's site certainly sound like an Invitation to Treat without explicitly saying it.

Classifieds: If you create a Classified Listing, you may choose to discuss with any enquirer, or offer or sell to any buyer, at your discretion.

Section 4.4 Comply with our policies

Terms & Conditions