I agree with going over and talking to the other party, but what the heck do you do when it's right at shooting time and here comes that late-arriving party of three? I've had more than one hunt ruined at Pt. Mouillee by late arriving parties. Not much you can do when it's shooting time and they are still setting up dekes, most often downwind of you too.
One example. Last year, second week of the MI season, set up at least 90 minutes or so before shooting time in the Vermet zone at Mouilleee. Wind was right, got all set up, waited until shooting time. Two guys show up 5 minutes after hours, throw some dekes out, and just stand in the water, not in the reeds or brush, but out in the open, behind their dekes. They were on the west side of the marsh, probably 150 yards away from us, downwind. Without face concealment, they were shining like beacons in the night. As we called in several groups of birds, these yahoos would shoot at them as they swung down wind to turn and come back to us. After getting rained on with shot for about the 6th time (several of the shots were taken 10' or so off the water), and watching them shoot all the birds we were calling, we picked up and left.
Now tell me how I'm supposed to handle that one. These guys obviously were not concerned about our safety, nor did they have a clue that they were shooting at birds that were decoying to us. They did not have the courtesy to set up in a section of the marsh that was open (there were other spots they could have taken) and they were late.
Heck, in hindsight, maybe they accomplished exactly what they wanted to have happen. Downwind some group and shoot their ducks and get an extra hour of sleep before heading out. I was livid, but we purposely did not go over to them, because I didn't want a bad situation to get worse. In talking with one of the DNR guys later, he told me "Welcome to Pt. Mouillee, it happens all the time here." That didn't help....