Even if you listed your vehicle manual in an inappropriate category such as for example.....electronics.....buyers would still find the listing via their keyword entries....as you know if you were enter the word Chevrolet, you'd be presented with all listings featuring the word Chevrolet....add the word Impala, and you'd see all listings relating to Chevrolet impala....placing the listing into the "appropriate" category will not really make much difference to the results returned unless of course a potential buyer is browsing Ebid by way of categories only (very unlikely).
Your disappointment in relation to selling on this site is due i'm afraid to not enough prospective buyers knowing of the sites existence in the first place and this is the barrier to healthy sales over here.....by all means tweak your listings by way of keywords, photos, prices, shipping deals....but in the end if no one is viewing these then its all rather futile.