How do I know my copy of Windows is legit?

Hi I've been buying and reselling laptops off of ebay for awhile but recently I got an email from Microsoft saying that I was reported to sell a component that doesn't have a valid copy of Windows. How do I find out that my copy is valid? I'm assuming that the copy installed has to match with the OEM sticker on the bottom? How would I find out if the sticker matches with the software?
I have 4 laptops here right now and I used JellyBean OEM finder on one that I was almost sure had a valid copy but the 5 group of numbers from Jellybean didn't match with the sticker on the bottom. I just want to make sure I'm doing this right. I have no problem installing Linux on computers that are not valid.

 

Hi no it doesn't look like the email came from an attorney, but through their compliance department. They stated that I "may have" distributed an illegal computer. I never sell software, just computers. I'm assuming it is legal to resell computers with Windows as long as the software installed on that computer matches up with the COA sticker on the bottom.

 

OEM installations from companies like Dell, HP and Gateway rarely match the COA number on the computer. They use a blanket license for the installation and provide the COA as a legal requirement.

I would question the validity of the email you received. I sell computers all the time with the OS on them that was there when they came to me and have never been questioned.

 

Hear read about the genuine advantage Tool Basically if your able too download updates from the web site your computer should be Genuine No if and or butts about it
http://support.microsoft.com/kb/892130


How does Windows Genuine Advantage validation work?

The WGA process is quick and easy. It collects no information that can be used by Microsoft to identify or contact the user. The validation process includes the following steps:

• Upon your first visit to the Microsoft Download Center, Windows Update, or Microsoft Update sites, you receive a message requiring you to validate your copy of Windows.
• You are prompted to download an ActiveX control which checks the authenticity of your Windows software. If the Windows validation is successful, the control stores a special license file on your computer for future verification.
• The validation process electronically checks for several known counterfeiting methods. Generally, you do not have to enter any information during this step.
• After successful validation, you may continue your download.
• WGA Notifications is an anti-piracy tool that performs the WGA validation check and notifies you if you are not running genuine Windows.

 

I know the WGA is supposed to be the definitive answer but I have had it flag several workstations as pirated software. In every case, a call to India . . . oops I mean Microsoft yielded a new code to reactivate the OS with no more hassle then being on hold for 20 minutes.