As said on the previous solutions, the photo and Google method is best for Grab Bag rounds. This is best achieved in a 'Party Game' match with two profiles using a single controller.
To unlock this achievement:
1. The primary profile used to play this must be the profile that you wish to unlock the achievement with. So if you have multiple profiles on the console, you must 'Join Game' by pressing 'X' on the start screen with the profile you want to unlock the achievement with.
2. You must answer every
question right in a five round quiz. This includes Grab Bag and Close Call rounds.
3. For Grab Bag normal, you must get a correct answer on every try with your primary profile. You do not need to get all the correct answers there are, but if you do, this will also net you the Greedy Grabber achievement. If using two profiles and you are confident of the answers, then simply select a wrong answer with the second profile and select all eight correct ones with the primary profile. If you are unsure of an answer, you can select it with the second profile; if it is correct, you will still get the achievement as long as you don't select an incorrect answer with your primary. So technically you can get four correct answers with each profile and still get the achievement.
4. For Grab Bag Blitz the above still applies, however you cannot get the Greedy Grabber achievement. This is because - as it states in the description - there must always be enough correct answers for everyone. Therefore when only one correct answer remains, the game will finish and you will not be able to get all correct answers with one profile.
5. For both Close Call and Close Call Blitz, you must
get the top answer on the board; merely getting a better answer than the second profile is not good enough. The only exception is if the top answer has already been selected, in this case selecting the second top answer will still count. This is useful if you are unsure and stuck between two answers. Simply select one with your second profile and the other with your primary; as long as you get first and second it will still count. This is a handy trick, as even with Google at hand, some of the answers are quite ambiguous.
Final tip is to pause and use Google, which you should already know
However, some of the answers are wrong on this game, so prepared to be annoyed when you've Googled an answer, you know it's right, but you still get it wrong on the game
Good luck and I hope you find these tips useful.