I think it's good to wonder WHY the vet is 'curious'. Perhaps the problem is more a matter of communication than of the vet wanting to do unnecessary tests.
As an example, a friend of mine had a lame horse, and its xrays showed some arthritis in its foreleg that it was lame on, so the owner was assuming it was a little arthritis, but the vet wasn't convinced and wanted to do more. It was slight and it came and went, worse some days than others...HOT days...weird? Well, the vet kept very politely dropping little hints about, gee, I'd sure like to know what is up with this horse, whenever he saw the horse. The owner was like some people here - very suspicious of vets and unwilling to go further into a diagnosis. Then the horse's coat started to get rough, and his ribs started to show, and he developed a very slight cough. The vet wanted to do tests - ON ITS HEART. The owner was furious - 'he's LAME and has a COUGH!'. Well, it turned out the horse had a heart condition. The hot weather was stressing the heart - and lameness in a right foreleg is not at all unheard of with this particular type of heart problem.
The barn trainer ignored a gelding that colicked frequently at shows. Kept pestering the owner NOT to get the vet and get it explored, THAT HORSE was just a wimp! Vets know nothing! They just want to get your money!
Well, it turned out that the lady's horse had an enterolith - a huge ball of minerals that had formed around a nail stub it had swallowed several years before. The body does that, tries to surround a sharp object. THe enterolith gradually increased in size and dragged a loop of bowel down and strangulated it. The horse died a horrible death, at a show, and it was a horse the woman had spent YEARS training, she had no money and had done all the work herself, it was a horrible horrible waste and she was never able to recoup the loss of that horse. A simple rectal exam would have probably identified the problem and a surgery could have been done before a crisis and death.
There is a point, where one has to stop being suspicious, saying 'all vets are crooks', and starting to think that gee, I need some help with my horse (and to move away from that barn trainer!!!!, LOL!). Find someone good, trust them, fix the problem before something goes very wrong or someone gets hurt. That's the thing about sick horses. The horse hurts, but someone else often winds up getting hurt too - the rider, the barn help, the trainer.
There are indeed a great many different sorts of horse care styles.
Some people are ridiculously fussy and are constantly seeing things that don't exist and calling the vet for the tiniest things.
For some people, the horse is a member of the family, and if it needs care, it gets it. If he's lame, he gets treatment and is rested until he's not lame. If he can no longer be ridden, he has a 'forever home' at their farm.
For others, they go even farther. The horse is an athletic partner, and even slight lameness or heat or swelling gets treated very immediately and specifically. They get xrays every six months as a routine, and review them with the vet. The vet is their partner in making the horse into a top athlete, and they don't even mull over the cost, because a few thousand dollars a year for care of a half a million dollar athlete is nothing.
Some people simply don't believe in treating lameness or in tending to their horse in that way. One gal told me she would have her horse put to sleep if the vet wanted to bill her over 250 dollars for - for ANYTHING to do with the horse. 'You baby 'em and they turn into wimps' she said, she didn't believe in getting wounds stitched up (even big old gaping ones) and if a horse became lame or had a bad leg injury, she sold it to the killer auction.
Somewhere in there, among all the different attitudes people have about vetting their horse, there is a practical sensible approach. Not overly cheap, but not fussy, taking care of the animal, and making rational, reasonable choices that are in the animal's best interest and keep it comfortable and working appropriately much of its life.
All vets are not created equal, for sure. But there are many times that I think very, very sadly, that people don't know as much as they think they know, and sometimes they really do need to have a little bit more of an open mind, and a little bit of respect for someone who has education and experience.