I would be extremely cautious about buying any passes on eBay.
First of all there is no way that you can determine, other than using a card reader ad WDW, what is actually left on the pass.
There are certain passes, such as Convention, which expire ten days after first use and are dated. Others, such as the 10-day World Pass expires 21 days after first use AND requires a finger scan. Likewise the multi-day, non-hopper passes expire a certain number of days after first use.
If you buy on eBay and there is a time limit to a pass, you have to condier the following timetable: Date of first use, when was it put up on eBay, when do you receive it in the mail, when to you get to WDW; timing would be almost impossible.
Anyway, I've never heard of a WDW pass with a 14 day expiration and that inclludes being very familiar with WDWIG (now AllEars.net) and MouseSavers.