If the original purchaser registered the game, you will not be able to do so yourself and thus won't be able to get updates or play online, so it is not advisable. E-bay copies are also frequently bootlegs using "used" or "foreign version" disclaimers just as an excuse for not including or including a nonworking serial.

Thanks for all your help!  I just tried the demo this week and I think I'm leaning towards a purchase.  I guess I might just have to bite the bullet and buy it...

General rule of thumb with stardock games - buy them new and you can play Multi-player and get content updates/patches. But them second hand and you are limited to single player/LAN using whatever is on the disk.

Hence it is better to buy them... I am finding it is cheaper for me to buy them via Impulse then get them in the store unless the game has been out for ages (I am in Australia). I can get DG online (digital version) for about 30% less then in the shops for a box and disc I will probably lose...