Well Spotting bootleg DVD's is usually hard to do.
One of the best ways is price, if it's too good to be true, it is. Another good way to avoid bootlegs is to avoid Ebay. You can have moderate sucess finding legit Region 1 DVD's but finding legitimate soundtracks and Region 2 DVD's is near impossible.
One of the easiest ways to tell on ebay is a DVD is a bootelg is to look for a region code. Auctions claiming DVD will work on any region DVD player will almost always be a bootleg (There are several legitimate anime DVD's with no region code, but only a very very small handful). Your auction has a region 1 code, it's probably OK. Bootlegs often will feture english AND Chinese subtitles, but no dub track. Nearly every legitimate anime DVD release in the USA has a dub track (Few exceptions).
Another easy way is check box art, and compare it to palces like
www.animeondvd.com or
www.amazon.com Bootlegs on DVD's often have different box art covers.
AVOID complete seres on Ebay, these will almost always be bootelgs, and will usually sport the "works in any region" description.