Is this legal? A situation that occured during a home game

Home game with players A, B, and C.

On the river, Player A makes a raise to 90.
Player B folds, thinking Player C might still call.

Player C is now debating whether to call the 90.
Player B, convinced that Player A is bluffing, offers Player C 30 chips to help him make the call and "catch the bluff."

A. Is this even legal (in a poker ethics/rules sense)?
B. If legal, should it be enforced or allowed?

Curious what others think — is this a clear angle or just casual home game fun?

I wasn't in the hand, but I think it was uncalled for. Bet sizing take into consideration the stacks of the opponnets, but the table was debating (we're all friends) so here we are now asking you guys to enlighten us.