I'm a confrontational person so I say call them on it but tactfully.
In my usual foursome, I'm typically the one offering shots on each side and typically I take money. We play for quarters and everyone is pretty honest and occassionally you'll have a questionable score mentioned. Usually, it's cleared up with 'wow; nice bogey. I thought you were in jail' or something like that. Then that gets them counting the shots and a stroke or two is remembered.
We play skins so if I bury one OB or in the drink, most likely I'll declare 'guys, I'm in my pocket but am going to finish the hole by dropping up near you guys in the fairway/green'.
Years ago, a pseudo friend and I played for money with some questionable scores being claimed. After catching him claiming a par after using a footwedge and picking up a four footer, I told him 'bets are off.'