Here's the deal: GW's lawyers search Ebay for "brand spamming", which means using a name brand in your title when the item you're selling isn't made by that company. You can research this through Ebay's HELP page. It is a violation of law, and when GW informs Ebay of a violation Ebay has NO CHOICE but to remove the listing or they risk being sued.
You ARE allowed to use a name brand in your DESCRIPTION (which does include the optional SUBTITLE) for "comparative purposes", something like "Great for use with Warhammer 40K". But unless the item you're selling was made by (or is otherwise endorsed by) the company, you are NOT allowed to use the company name or any of its trademarks in your TITLE.
The legal reasoning behind this is that if you are using a name brand to make money with an item not made by the company, you are benefitting from the reputation that the company has spent millions of marketing dollars to build. You are, in effect, stealing advertising from them. WARHAMMER is a trademark of GW. To use any company's tradmarks you are required to give them a piece of the action by buying a liscense from the company to use their trademarked names. Otherwise you aren't allowed to make reference to their name(s). And the cute trick of saying "NOT MADE BY Warhammer" doesn't work either, you're still using their name to draw buyers to your listing. Those listings will be dropped just as fast as any other!
It's helpful to put "War Gaming Terrain", or something similar in your TITLE, since many people are aware of this problem and have modified their search strategies. And BE SURE to reference "Warhammer" in your description and in the body of your listing tell people to check the "search title and description" box on the Ebay search page, otherwise when they search for "Warhammer Terrain" they'll get ONLY listings that have "Warhammer" in the TITLE, missing all of those that do not.
FYI, multiple violations WILL get your account suspended and then you'll have to, among other things, sign a LEGALLY BINDING affidavit stating that you will never violate that rule again in order to get your account reinstated. So BEWARE!
FYI, this rule applies to ANY name brand; for example, if you made a garage for Hot Wheels cars, technically you're not allowed to say "Hot Wheels Garage" in your TITLE, but unless Mattel complains to Ebay you will likely be left alone. Unfortunately Hugo Prichart (GW's lawyer) is a HAWK and once he discovers you he'll be all over your listings for the rest of your natural life!
Hope this was helpful...