Q: i just bought ipod 5 on ebay and the seller did not know passcode can the apple store fix this problem

No. Return it for a refund. It is worthless to yo except as a poor flashlight.

It is likely lost or stolen.

Contact eBay if the sell does not cooperate.

The get him to recover the password.

How do I change or recover a forgotten Apple ID Password?

If you've forgotten your Apple ID Password or want to change it, go to My Apple ID and follow the instructions. SeeChanging your Apple ID password if you'd like more information.

The get him to remove the iPod from his account

Find My iPhone Activation Lock: Removing a device from a previous owner’s account

Place the iOS device in Recovery Mode and then connect to your computer and restore via iTunes. The iPod will be erased.

iOS: Forgot passcode or device disabled

If recovery mode does not work try DFU mode.                        

How to put iPod touch / iPhone into DFU mode « Karthik's scribblings        

For how to restore:                                                             

iTunes: Restoring iOS software

If problem what happens or does not happen and when in the instructions? When you successfully get the iPod in recovery mode and connect to computer iTunes should say it found an iPod in recovery mode.

The previous owner still has to remove the device from their account in order for you to activate the iPod.