Buy posting a list of such items, the price automatically inflated as people started to ask more for any they had, whilst some others would buy up the cheap stock and reprice them higher.
However as you are looking to help and many people know about the following items ...
...below level thirty there is not much that you need to look out for, people would though appreciate it if you listed hydragen-carbids on the market rather than selling to the store. To a lesser extent the same can be said for crystal plates and vampiric herbs.
KmS :)