@Quercus:
You and I might be able to tell whether or not the dog is bluffing…but do you want to put the person you are advising at risk by suggesting they try to figure it out on their own?
Oh, I absolutely agree with you there. People have to do what they are comfortable with, and if they are not confident it won't work out well. I spoke of my own experiences, and I admit that I (and most of my friends) am "old school" because that is very much our generation. Quite frankly, a dog that snarked at someone when I was a child would probably have been dismissed with a boot in the ass, but incidences of snarky dogs were extremely rare, for a whole bunch of reasons that no longer apply in our modern world. We never had one, and I didn't know anyone else who did.
How you handle the dog as a pup definitely comes into play here. If a pup has a very clear idea of where he fits in the family, the idea of defying anyone will simply never occur to him as he gets older. As a teenager I used to walk and train dogs for folks. Never suffered a bite from any of them, or a snark for that matter. As I said, different times. That kind of behaviour was simply not tolerated by many people "back in the day". (maybe breeders attended more to temperament back then? For sure, the temperament in many breeds has deteriorated, especially any that became popular)
The best advice for anyone who is unsure how to proceed is likely to work with a trainer or behaviourist, but even that can backfire if you use the wrong person. I have seen "positive" methods have unintended, negative results, I have seen people create fear biters with harsher methods, and I have also seen success stories both ways, so nothing is written in stone. I don't think anyone is likely to find a magic answer on the internet, and all advice needs to be taken with a grain of salt. But when in doubt the safest thing is distraction, not direct confrontation. I do not go that route because I haven't had to, and in an emergency (the dog has something that is dangerous to him) I would never hesitate to intervene, whether a bite was a likely result or not, so I just practice what works for me and in fifty plus years it hasn't let me down.