You art definitely has that "old school horror T-shirt vibe" to it, which is cool. I do think they look a little "dirty", though. I would recommend trying to work in inks (
Rapidograph works for most people, lots of different sizes and available in most art supply stores..or your local Amazon, obviously).
Some people can make the strait up pencil shading work, but in your case, I think you need to move up to ink especially if you intend to try to sell them (which obviously you do...btw, it's a LITTLE tacky to have your links go directly to ebay pages. If you want to sell your originals, just put on your site that all originals are for sale and to email you if interested. If you want a true gallery, those thumbnails should just enlarge to bigger images. I felt duped :p ). Hell, I can tell that you are even stippling quite a bit, which will be gorgeous in ink.
Content wise, it's fun art...like I said, reminds me of that oldschool look and I like that. When/if you do try inks out, just remember not to press so hard on the pencils so you can erase them and leave the ink. It'll look a lot better to see black and white instead of dark gray, light gray, and mushy smudged gray. ;)
-D