It is a difficult issue.
I've done a few large group block and drive paid hunts on wild birds in South Dakota, with the owner/operator and individual guides. The group decides and usually gives the tip in cash to the owner, in vision of the guides, for the owner to distribute. It's more of a business relationship, and the tip is usually on that basis.

That's different than a guide and his dogs with you and a friend and your dogs.
I tip/reward based on attitude and effort. Not the guides fault if it's a bad day or the weather doesn't cooperate.

My best experience was with a family that ran a pheasant operation on their property near Presho, and the owner and his wife were the guides. After the hunt they provided snacks and drinks in their home.

One point; communication is critical in avoiding disappointment. Let the guide know what kind of hunt you want (and the experience and physical shape of you and your friends) and ask appropriate questions to understand exactly what the guide is offering.
It's important to know ahead if your group will be part of other groups, who may have new, unsafe, or hung-over frown shooters.