If you come accross brand new items that are unusually low, do some research on the seller, look at their feedback from buyers, click on the items that they have sold, check that they have not just sold 1penny items ( this is done to gain feedback ), ask yourself do they seem to be selling stolen or copied goods, check the quality of the items. Do they seem to be trusworthy And remember...
IF IN DOUBT LEAVE IT OUT
Also check that they offer good aftersales service as this may be very important for you.
GOOD MANNER THEY SAY GOES ALONG WAY, WITH EVERY TRANSACTION YOU SHOULD FEEL SATISFACTION.