Am I wrong to deny my roommate money?

My friend “Josh” is out here from the east coast. I asked my roommate “Sam” to rent a car for him since he’s under 25, the security deposit would $500 instead of $300 and the fact neither of us have a credit card available. Sam wouldn’t have to pay for anything cause we’d only be using his info. Sam agreed. Josh sent me the money and we split the security deposit. Sam doesn’t trust anyone or the area we live in. When we went to get the rental, Sam added insurance, something Josh and I didn’t intend on getting nor did Sam inform me of wanting. I ended up dipping into half my rent money to cover insurance. Now we returned the car Sunday and will be receiving the security deposit in a few days. Sam wants $100 from the deposit because he put himself on the line for someone he doesn’t know and that of something happened to the car it would be on his record or whatever Nothing happened to the car, it is completely fine and Josh said he’d pay for anything if something did happen. I told Sam no and he didn’t like that. Even today, he’s still upset and makes it known. All my friends and my sister say I don’t owe him anything and my dad said I should pay him back for doing him the favor. Dad also said $100 is a bit much so perhaps $50. Am I wrong?
Am I wrong to deny my roommate money?
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