Clearly this is a concern we all must face once in our lifetime. The purchase of falsely advertised products by any given site. Unless you know from the beginning that the speak was used and or damaged. I can not vouch for Anker in this case simply because this was not an Anker issue only an Anker product as sold by another site.
Firstly, and this is very important. I would contact eBay and file a claim report implicating those who sold the speaker to you. Also posting a review on the a sellers profile page with all the details of your concern.
Second of all, I would send a support message via Anker's site and inform them of what happen view the bogus eBay seller. I can not say if Anker will do anything to correct your issue, but one can never know until they try.
The point here is to contact all thsoe who need to be contacted about thsi bogus seller and have their account suspended is this can be done. But as we all know buyer beware.
As I was informed earlier today.. make sure you look for the official tag name as listed on sites like Amazon etc. If you do not see an official Anker tag on web site or in retail stores.. I would avoid these locations unless they have been given permission to sell Anker products.
Lastly, if you locate a site or business who has posted details about being an official Anker product retailer.. Before you buy, Contact Anker just to verify that site/business has been verified by Anker.