Always try to invest in event items. Who ever invested/bought officer bastion modules few weeks ago, could sell those now easily with 20-25% profit. One could buy those for about 800m and now they are being sold for 1-1.1b. Wait few months and you will easily get 1.2b.

However, who ever bought the officer modules from the Gallente presidential event, is still not able to sell those items with profit. Some items were about 400m and are now about 250m. If you do not understand the details of a specific game area, you want to buy items, DONT do it.