Hunter I may be wrong, but when he says dirty I think he's talking a grungy, more worn look. Think any new game thats been out in the last few years.
Take my stairway, I just made. It shows no real dirt but certainly shows plenty of signs of ware.
The textures your creating though a great start, are no where near the point of selling. Seems quite a few people all want to sell those packs and make that money. I'm sure I could sell a pack as well but I'm more interested in actually making a game. I suggest mastering your craft by creating enough media for a game. This would give you plenty of practice. Don't be in such a rush to get in peoples pockets. Though fine for personal use there no where near profesional quality.
Good luck
Loc
(EDIT: Cross posted with xplosys)