adobe photoshop - What makes a design professional?

Can anyone define why something might not look "professional"?

What differentiates between professional/unprofessional designs?

I have clients who have said my design does not look very professional. I followed all the things to make it professional - maybe I don't know enough about design? I have seen lots of "professional" design templates that look easy & similar to mine. Most of the time, when I don't have any way to go, I follow these template designs - but when I finish I get feedback that "This doesn't look professional". This doesn't help me though. Does anyone here have real-world help/experience/suggestions would help me regarding looks, font, style... everything. Please give me a way!

In short:
What makes a design professional?

Answer

I made this another answer since this is to comment on your design:

You tell us that you can easily recreate professional templates. In fact i doubt it. You really have to learn a lot about webdesign. Seriously far to go, but you are eager to learn and therefor i made this mockup to explain some things. This is not to bash you, seriously no offence meant, i am just being honest.

The basic story is that it is lacking alignment and depth... alot of depth.

I will also include one of my designs i am currently working on width a grid overlay so you can see what i mean. It is far from done, but you will get my point. Please do not use parts of the design i am working on since they are copyrighted.

Take a look at how i create depth with smooth gradients, textures and shadows. Besides that, take a look at how it is spaced.

Edit: Just so you know, i editted the width for copyrighting. So this isnt in real aspect ratio.

Hope this helps you.