I choose to believe the evidence. Obviously, you cannot trust Zaka. Finkelstein usually provides quotes or references so you can verify his claims, so I tend to trust him.

No one said the IDF was responsible for all of the dead. But anyone who understands deductive reasoning should grasp that Hamas wanted hostages to trade for prisoners, while the Hannibal Directive was created to ensure Hamas would take as few living Israelis as possible.

As for general sources of information, you might also do a little googling about hasbara.