As you usually walk alone, you will know to close a gate behind you. What if a gate was open when you came to it, how would 'tail end Charlie' know if the gate was opened or closed when the leader went through it. So who appoints a back marker, does there have to be a leader?
I don't think being scammed for a round of drinks is really a walking issue, possible a point of conversation in a bar. Just my opinion, but there are many bad social traits that give the visitor to the countryside a bad image in the eyes of the occupier. Such as bad parking, should access be restricted because many do not know how to behave towards each other. If you walk with a group your collective behaviour has a greater impact than the lone walker.
So an interesting tale comes to mind; A farmer was drenching his sheep (giving them medicine), he was on his own, so he erected the working pens between two fields and let the treated sheep run out in to the adjoining field. Elsewhere a footpath crossed the boundary between these fields and a party of walkers went through, the gate got left open and the treated sheep became mixed with the untreated sheep.
The farmer should have marked the sheep as he drenched them, cardinal rule. If he had sent an employee to do the job and there had been an accident he might have considered negligent for not sending two to do that job and there would have been someone to do the marking.
I knew the farmer, who actually was the originator of this story, but I have heard the same story from many other sources. Many other farmers retell it to blacken the name of walkers and use it to backup there own grievances. So collectively they are lying to to score points.
Perhaps this is a lesson that groups leave bigger footprints.