More than 86% of fatal dog attacks are done by this kind of dog:

[KurtNYC]

Un-neutered males.

Approximately 92% of fatal dog attacks involved male dogs, 94% of which were not neutered.

http://www.americanhumane.org/animals/stop-animal-abuse/fact-sheets/dog-bites.html

I own 2 dogs and have many friends who also own dogs. We go to dog parks. We socialize with every type of dog. I usually rely on other owners to say whether their dog is cool with meeting other dogs, or to set any limits. A fair percentage of owners mis-read their own dog -- tail between the legs, backing up but they drag the dog forward to mine or won't let it back up -- that's when I back my dogs up and decline the greeting. A scared dog will bite more readily than a confident relaxed dog. We have all heard about "fight or flight" but many dog owners don't apply this knowledge pragmatically: if your scared dog can't 'flight' then its only option is to bite so make sure both dogs have room to back up.

When we are approaching a new dog, the second thing I look for is whether or not it is neutered. If it is NOT neutered then I don't care what the owner says, there will be no greeting. I will cross the street or do whatever I have to do to avoid contact.

( The first thing I look at btw, is the body language of the approaching dog and its owner and how long their leash is. )