oem software

whats the difference between the oem software like vista you find on dhgate and the product you buy in stores. And how can ebay or customer know its not official

Difference is that it wasn't made by Microsoft, so it's an unauthorized copy. If the buyer decided to call Microsoft to report a bug or problem in the software, and M. asks for the serial number, and they find out that no such serial number exists, it will become evident that it's a copy, and you're ass is toast. The end.

Almost all things from china = Fake/replica... that is why you are screwed. Microsoft and Adobe products are VERY hard to list on Ebay due to all the fakes going around.. i know very well from experience.. i wish you the best however

OEM = Original Equipment Manufacturer, OEM software is supposed to be shipped with a new computer or shipped with hardware that is required for a PC to run, like a motherboard.. etc..