irregular braking rim problem?

[Chain-L]

Bought a new bike and have had problems with irregular braking since day one. Feels as if the wheel is not true, but have taken it two different shops and the wheel is true. When I replace the wheel with a test wheel, all is good. The problem must therefore be with the rim.

 

Two bike shops have smoothed the rim and pads but no luck, actually made it worse.

 

The only other thing I can think of is that there is a slight widening of the rim through a manufacturer error. anybody came across a similar problem before?