IMO every animal that isn't obviously being used by a blind person as a seeing eye dog gives me reason to doubt that any service animal or ESA claim is real, although I admit that some are much more obviously not real than others. Distrust and verify.

Not from Europe, I've just lived there at times. It's interesting that in many European countries, including France and Germany, it's always been common for people to take their pet dogs into even very good restaurants. In fact, I once witnessed a dog fight in the middle of dinner at a Michelin three star restaurant that catered to dogs by serving them Perrier in sterling silver bowls.

To me, the PTSD dogs, hearing assistance dogs, epilepsy/diabetes problem detection dogs, dogs that fetch items for people in wheelchairs, and even the miniature horses that provide stability and support for those who otherwise would have great difficulty walking are very very different from the garden variety untrained pets pretending (even with documentation) to be ESAs, yet often it isn't obvious that such genuine assistance animals are more than extremely well behaved pets. Few people would have pets if the pet didn't provide some measure of support and companionship and I suspect that most people arguably have some form of a mild psychological disorder as I've never heard of a therapist refusing to see someone on the grounds that the person doesn't need or wouldn't benefit somewhat from some therapy.

.....and anyone can easily buy such documents over the internet, perhaps by answering a few questions online and/or having a quick phone call with some "licensed professional" specializing in this.

I'm not saying that I want to see anyone's private information, but if I see an animal on board, unless it's a seeing eye dog, the odds are that it's a fake ESA even though it might be wearing a (fake) service animal vest. I'll believe what I want about these animals, based on "preponderance of evidence" if you wish.