Personal recommendation is the key.

I jumped into the water from a rather big height ten years ago, was
sort of flexed backwards and had pain in the lower back afterwards.
For a year I stil felt "something" there, but my doctor told me that
was normal and just a strained muscle. He was right.

Then two years ago I had a period of terrible arguments with my then
girlfriend, and one day got a sharp pain in the exact same spot,
mid-to-left lower back, next to the spine. Lay prostrate on my floor
for two days and couldn't get up, the pain was excruciating. The
doctor who came to see me asked if I had done any movements that could
have provoked it? - No. Was I stressed? - Well, yes! He said that
everybody (every body) has a weak spot somewhere, and that is the
place that gives in during stressful periods. So that lower back area
is my weak spot. He didn't explain what he thought caused it, but got
me medication and the pain went away by itself after some days.

Got rid of the girlfriend, so when I got a pain there again half a
year later it was in fact due to sports, a bad movement during a
squash match. It was the first match after the summer holiday, so I
was out of shape, but my partner had been practicing secretly .

This time colleagues recommended a chiropractor (here in Belgium
they're called osteopate or kinesi-therapeute) and I went to him. He
was excellent. Asked me about my history of pain in that area and I
told him the above story. Then proceeded to twist me around a bit on
his couch, explaining exactly what he did and also perfectly
predicting how I'd feel after each movement. "You will now be able to
lift your left leg, but not your right", etc. At the end he told me
the pain would be 3/4 gone by the day after and totally gone three
days later, and he was spot on.

He also proceeded to explain to me exactly what was the issue. A long
muscle going from the inside thigh through the pelvis attaches at its
upper extreme to the lower back. He said it was the top attachment
which had been weakened and now sometimes would get inflamed when
over-stressed. I was so relieved to hear it wasn't a spinal issue, a
partly slipped disk or something. At the end of the visit he told me
of a very particular exercise that would work pin-point on that very
muscle attachment. I use it from time to time.

Best thing about this fellow is his total knowledge of the muscles and
bones of the body and his willingness to patiently explain me things.
I can only say I consider him a true artist. And he took all of 25
euros for the half hour I was there.

I'm sure there are a lot of incompetent quacks out there, so personal
recommendations must really be the decisive issue. Sorry for the
long-winded story...