<…> How is the trust used? I get the impression people use this site as platform for buying/selling in addition to just posting questions and answers?
It it’s origin, the system was aimed at evaluating a profile’s trustworthiness in commercial transactions with them, although over time it has been used for a wide variety of things that are not aligned to that spirit (as the provided trust type and feedback are freeform), retaliation being one of them.
Some boards show those numbers alongside the profile summary to the left of each post, whilst others do not. Nevertheless, if at any point you want to see somebody’s trust score, it is better to go to his profile and click on his Trust link in order to access the detail of the Feedback behind the scores. There can be both Trusted Feedback (that provided by the Default Trust Network (DT) or your personal Trust Network – whichever you have), and untrusted feedback (provided by people that are non-DT or not in your personal Trust Network). Read the feedback properly on both listings, and decide for yourself whether the feedback is relevant to you.
Bear in mind that the numbers you were inquiring about may change from one person’s view to another, and even over a short period of time (DT lists change every month slightly, added feedback, etc.). The majority of people all have a DT view (Default Trust), and therefore see the same if the Trust ratings. If you have a customized personal Trust Network (there are only just over
4500 people that do), then the ratings will possibly show different numbers in the Trust scores, and the Feedback may have shuffled around between both lists (trusted and untrusted feedback).
The links provided in this thread will help you to understand the specific details if you wish.