In season 3 when Oliver loses his fight with Ra's Al-Ghoul he is stabbed right below his chest. However when we see him return with bandages the wound moves lower around the abdomen area.
During the fight, Ra's Al Ghul catches the sword with his hand. In the next scene, the hand is turned in the opposite direction.
When Ra's disarms Oliver, he takes the sword from Oliver's right hand. However, in the very next shot, Oliver has a sword in his right hand with his left hand empty.
Before Ra's stabbed Oliver in his chest, he stabbed him in the side of his abdomen to weaken him, and drawing blood. However, after the stab to the abdomen and before the stab to the chest, the scene shows the sword is completely clean with no blood on it.
When Oliver starts bleeding from the mouth after being stabbed through the chest, several different shots are shown wherein the blood on his mouth and the open wound are nonexistent.
Matt Nable's stunt double is seen multiple times during the final fight. In fact, in almost all non close-up shots of the final fight, it is clearly seen that it is the stunt double who is playing Ra's instead of Matt.
When it's discovered that the DNA on the arrows that killed Sara are Oliver's, Oliver says that it is Malcolm that killed Sara and set him up. Diggle responds that it could not have been Malcolm as he - by his own admission - was in Corto Maltese at the time. However, Team Arrow do already know that Malcolm was in Starling City just prior to Sara's death as Nyssa revealed that Sara was in Starling City to investigate Malcolm's presence there and Sara had taken photographs to back this up.