When Miller throws explosive into the German patrol boat's engine room it explodes in sheets of flame, etc. However, there is no damage at all to the fishing boat - no scorch marks and no debris even though the boats are virtually locked together. At least the sail should have caught fire.
In the British army in those days Brown would not have been allowed to grow a beard - that's only allowed in the Navy.
When the fishing boat is stuck at the base of the cliff we see it tossing and rolling. However, when Brown is in the hold there is no movement. Also when the men are unloading their supplies the boat is obviously fixed and stationary.
Mallory makes a point of speaking Greek to the Germans in response to their commands in English. Later, however, Maria tells the group 'hands up' in English before she knows who they are - and they respond! Later still they are sitting at the wedding when the Germans come. The officer speaks to them in English - this is before they are aware that there is a traitor in their group.
Why didn't they respond in Greek?
When the girl is killed by Maria we see a shot of her head and shoulders. She is not shot in the head so we can only suppose that has been shot in the heart (for her to die so quickly) but when Brown checks her out there is no blood and no exit wound on her back. So where was she shot?