I think it is bad form to offer another player advice during a roll-up game of bowls. But sometimes it is possible to improve a person’s performance without saying a word.
Recently, I was skipping in a game of drawn triples. I had no knowledge about my other team members. In fact, I hadn’t ever met them. In the first end, I signalled my lead to deliver forehand and he brought his hand across his body in the follow through and the bowl almost left the rink after it cut across the centre line. This was repeated twice more, even though I was giving him grass with an allowance for this difficulty.
I never signalled for another forehand the whole rest of the match— always backhand, no matter what the situation in the head. Intuitively, people do not bring their arm across when bowling backhand. His weight was good, and he made a significant contribution in the remainder of the game!
Only afterwards did I tell him what he needed to fix on his forehand.