This guide is borne from my purchasing experience of this product.
Ear or headphones are often advertised on Ebay, however a number of points have to be remembered:
1) Is the headset or earphones really stereo, ask for a picture of the non-usb connectors which should show two bands on the connector ( our research involved many samples being provided with one - i.e. mono in both ears).
2) Are the connectors if non USB, 2.5mm or 3.0mm jacks? If the former, many laptops will need a convertor, but they will work in a Blackberry and other devices if 2.5mm.
3) Any bona-fide supplier will provide a guarantee, for example a simple post back and return policy for normal wear and tear. The items are low tech, and any reputable local supplier will support your purchase.
4) MAC users - remember to check compatibility as often your laptop is USB only.
Please contact me for more information, and if I can help in any way.