Also, the common wisdom goes that horses that are sold usually have at least one thing wrong because the best horses are kept, not sold or bartered off to the next owner.
not true. They might have something 'wrong' in the owners eyes, but many times the owner trains and resells, breeds, likes starting colts, was given a horse, had something change in their life, or for some reason no longer has the money. There are many, many reasons people sell. I have sold several because I like training, but wanted to move on to another horse to start when it was doing well under saddle. I have sold horses because I bought them young and they didn't turn out to be exactly what I wanted, or they were too short or tall, or we didn't get along extremely well personality wise, so didn't really enjoy each others company. I have even sold a horse because she was too easy to train and I got bored. I bought a horse(my current arab mare) that had a couple minor issues. The old owner practically gave her away. she needed work on standing for the farrier, wont take any medication by mouth and had a bit of a hard mouth. A tiny bit of effort to fix those things and she is the best horse you could ask for. Sound, sane, safe, safe, safe, I would trust her with my life. Never thought of bolting, bucking or rearing.
OP, I have sold many horses, for myself and friends, and I have never had a horse throw me while showing or throw a buyer. I have sold very few horses that I advertised as beginner safe, and they were virtually bomb proof and never offered to bolt, buck, rear or kick.
I've just been frankly shocked at how many people will declare a horse 'safe' even after it bucked them off and bolted (and not for any good reason, either, just because it didn't feel like being ridden). How on earth can you think your horse is safe if it just turfed you off and hightailed it?
there are lots of lying scums out there, in every profession, hobby and circumstance. For every seller that lies there is a buyer that over estimates their own abilities, lies about their skill level and tries to take whatever they can from the situation. I've been scammed by several buyers. I've had many come out that think its fun to come for a free ride on a weekend. I've had small items go missing after a buyer visits. I've come to feel that its "person beware" in every circumstance. Unfortunately it sounds like you found some of the bad sellers first.
Some horses are a lot longer on temperance before they start "trying" the rider or, finally "lose it" with a rider's lack of ability.
this is true. If you want beginner safe, make sure beginners have ridden the horse many times successfully before.