1)
Why did they tell him "Hacharesh Sim Yadcha Al Picha v'Lech Imanu"?
1 Chomas Anach: If you ask how we can steal, be quiet. If you rebuke us for following idolatry, put your hand on your mouth, for we will not accept [your rebuke]. If you are concerned for your wages, come with us, and it will be good for you - you will have more honor, and we will increase your wage.
2.
Malbim (18,19): (a) Regarding the theft from Michah - only five men took them. Had he screamed, the people of Michah's house would have protested. (b) Regarding yourself - be quiet and come with us, and you will gain - you will be Kohen to an entire Shevet!