Hi, yes, a different frequency is required. Newer transmitters have a switch and the receiver in the robot has to be changed.
When the neighbor purchases the LawnBott, hopefully he mentioned to the dealer that the neighbor has one. A reputable dealer will make sure the new LawnBott is properly configured at no additional cost.
If someone buys one used and installs it next to their neighbor, well, then they would have to pay for the reconfiguration.
Problems will occur like one robot will lock onto the other robot's loop during startup and give an error like "Out of Border", "Sync Error" or "No Signal". The problem could happen randomly or not at all.
Also, the two signals could create an interference signal that causes both of them to not work.
The best is to have them on different frequencies and avoid the problem altogether.
RobotLady