I can't remember the story line of the book but the cover was a uniform yellow and I distinctly remember the main character figuring out that the name of a company was the anagram of Aldebaran [star], perhaps Narabedla. It may even be the title of the book. Any ideas?
It's probably Narabedla, Ltd. by Frederik Pohl. The name of the alien-owned corporation that the book is titled after is the word Aldebaran (a red giant star in the constellation Taurus) spelled backwards.
There are a number of different cover designs for the various printings. Being you're in Belgium, I'm guessing you had gotten a hold of a copy from Victor Gollancz Ltd, a British publishing house (they seemed to like the yellow covers):