My response may be a little bit off-topic but first of all, I want to say that Default Trust shouldn't be the most important metric here! Because Trust is abused and this is the place where we are more likely anonymous. Default Trust and trust scores in overall may give a little bit boost in confidence someone to take first step in trading or trusting something, it's like gambling where chance of win is 90% but you don't know whether that 10% shine or not.
So my question is - how can members improve their trust ratings if there are no business trading opportunities in the forum?
Why do you have to improve trust ratings? It's just numbers and it's easy to fake numbers. Anyone can organize a good plan about how to boost their trust, even with trading. Someone may trade even thousands of USD just for trust score, it's like investment in your trust. But there are other people who have a need of trading and find this place a good one to trade and built trust naturally that they really deserve.
Trust system is dilemma here.