Not a bad looking sheath. Here are my views:
First thing that screams at me is the edge! I can't tell if the shiny spots I'm seeing are an attempt at burnishing or glue or? The edge needs to be sanded (by hand or power) till it is all smooth and uniform. Then burnished properly. As you can see from the picture, it appears the welt has shrunk a bit leaving the outer edges higher. This can be resolved by sanding, redyeing (if need be) and burnishing.
Next- The stitches. There was no stitching groove cut to allow the stitching to sit below the surface of the leather. This can cause issues with prematurely wearing the stitches, causing them to fail. Also, the thread used seems a bit small for the sheath.
It's hard to tell from the pictures, but it doesn't appear that the edges have been beveled. Beveling all the edges (throat, seam, belt loop) will give a more professional appearance to the sheath.
Belt loop looks good. Although I would have skived down the ends to blend them into the sheath more, making the belt loop not stand out as much and with the top edge skived, it allows the belt to be inserted without catching on the thick edge.
I would have brought the curve down a bit more, making it wider to where it comes to a point at where the blade starts. I believe this is more of an aesthetic suggestion vs affecting the overall use of the sheath.
As for the artificial liner: I would make sure that it's not treated with any kind of chemical that would cause a reaction with the steel (like chrome tanned leather will do).
How is the retention of the blade in the sheath? Overall it looks like a nice sheath, and a great first try. But, it has a mass produced look to it that could be remedied with a little tooling, even an extra groove cut next to the stitch line would give it a more custom appearance.
