I find it somewhat odd that SebastianSh is unable (or unwilling) to grant that simple request.

In other professions (web design, software development, etc) this is usually a sign of missing expertise. What kind of designer or programmer wouldn't proudly show his/her latest creations when asked to do so?

However, in this case there might be another reason. Maybe the customers don't want to be used as a reference? This leads to an interesting question:

Is it bad for business to publicly admit the use of SEO techniques?