How do you recognize a good coach?

You can't. Or at least, most people can't. They wouldn't really know the difference between, say, Cressey vs. me vs. the average globo-gym trainer. Most people's impressions of their trainers are predicated mostly on the trainer's personality and professionalism and looks, not their skills and knowledge.

But it's easy to recognize a bad trainer, even for the uninitiated.

Warnings signs (not necessarily 100% indicative of a bad coach):

• Doesn't regularly program squats, deadlifts, presses or pull (or some variation thereof) for most clients.
• Makes most clients very sore, very often. 
• Doesn't make clients sore, ever.
• Your program is predominantly on machines.
• Has a CrossFit Level 1 "certification" but no other qualifications, and has never coached anybody before getting their L1.
• Programs lots of crunches, but no planks or bird dogs.
• Does lots of curls on Bosu balls.
• Does lots of curls.
• Doesn't know most of these names: Cressey, Robertson, Hartman, McGill, Boyle, Dan John, Simmons, Tate, Wendler.
• None of the men can deadlift 2xBW despite training for >1 year. 
• None of the women can do pull-ups despite training for >1 year.

Note: most of these (although not all!) have applied to me at one point in time.

Actually, there is one rule of thumb for good trainers, but it's not really useful because the list is so small:

Anybody who's ever been excommunicated from CrossFit HQ is probably a good trainer.