See, Shadowrun GMs need to understand a couple things about Shadowrun:
1. Fixers live and die by their reputation. Fucking over their runners is the quickest way to ruin that. Ergo, any fixer who fucks over any runners will soon find themselves dead in a random ally in the sprawl, and not necessarily by the guys they fucked over.
2. Corporations run on a strict profit-loss model, which is why runners can even do their thing in the first place. Any exec who blew up a building to get back at a couple runners would find himself fired, demoted to being the personal assistant of the mail room intern, or volunteered for one of the company's "Behavioral Correction Programs." Hope he doesn't work for Aztechnology! Blowing up a building is a huge expense for no profit (less profit in fact), and these commie LARPer GMs need to learn this before they even think of running any cyberpunk game.
3. You didn't mention this, but GMs seem to like having Mr. Johnson fucking over his runners constantly. Johnson has a bit more leeway, but each one is different, has different goals, and works for different organizations. So why do so many Johnsons seem to come out of a Happy Merchant Meme Factory?