Cliff sensor reflector

I bought an AGDA Robotic vacuum cleaner which refused to clean my kitchen floor, backing out of the kitchen as fast as it could, terrified it was going to fall off a cliff.

A search of the net revealed two things>
1. This machine appears to be one of many coming out of a factory in China called Lilin ( http://www.robotvacuumcleaner.cn/ ) and also appears to be the same as the more commonly known brand Roomba.
2. There are many many complaints of Roomba vacuum cleaners going backwards when