My name is Jake, I am no expert & only just starting to dip my toes into the whole selling my own models so I'll throw my 2 cents in with the hope of helping.
I'll start by congratulating you on a great model, I like it a lot. I look at the wireframe shots and rate it A+ standard. But when it comes to the textured shots I struggle to see the 'depth'. I personally would focus on improving the textures, in my opinion the textures are just 'too clean'.
An Unwrap UVW modifier also would be good. The bricks are a bit weird looking, the more i look the more I see the difference in brick height as well as slanted bricks in the top centre. So a bit of geometry editing to manually bring out the bricks or a flat plane with a high detailed seamless texture.
I guess it all depends on what renderer you're using too. My personal favourite is the vRay renderer.
Hope my opinion hasn't been too harsh. Happy modelling, all the best... =D