Everytime a satisfactory sale is completed the vendor and purchasor award each other a point.
Buying second hifi from people that you don't know is always a bit risky but if the vendor has a reasonable rating it makes that risk a little less.
The problem is that on AVF most of the ratings and points awarded are for the sale or trade of DVDs whereas here it would be the sale of higher value hifi equipment therefore of much less use unless you have some serial kit changers.