From my limited experience of various forums I remember very very well a situation which occured on the Volvo Owners Club forum which ended in legal action where the complaints for and against a trader were discussed in great detail. It got very heated and should have been stopped by the Mods. It did not. When it went court copies were made of the discussions that took place on the forum. As a point of general interest I have to be very careful of any opinion I express relative to my profession as what I advise, if found to be wrong I can be legaly responsible. Evidence can be printed from these web pages and used. It has been known stateside that owners of forums have been required to produce membership details. Lets hope that never happens in the UK, but, I don't think we are far away. I think the option of only passing comments regarding good service is a good one. I can't imagine what would happen if it was permitted for deflammatory comments to be published about anybody it could get get very personnel. There is of course situations which occure where very bad service is provided and there is a dispute, you have written to the provider of this bad service and you publish the letter on a forum site after you have informed the provider you are going to do so. I would leave the final decision up to the owners of the site to make the final decision, I would not even burden the responsibility on the Mods.

Use the small claims / county court. It costs very little.
Cheers