The big scam is that since chiros aren’t allowed to write prescriptions, they try to sell you all kinds of vitamins and nutritional supplements.
The unfortunate part of the things like chiropractic is that they do work for some, but it's unclear why they work or which patients are likely to benefit or which to get hurt. And they tend to be a little less critical of other alternative treatments.
The same lack of clarity goes for nutrional supplements. Recent studies show that adding folic acid to the food supply isn't a good thing for the entire population.
It might be good for pregnant women, but woefully bad for other folks.
Even if chiropractors and other alternative docs tend to be a bit too uncritical of possible remedies, the mainline medicos can also push things without appropriate study. Pushing Folic Acid looks to be a rather large mistake. Pushing Vitamin D is going to be shown to be an even larger mistake.
see www.bacteriality.com for a newer view into the problem of chronic disease and an infectious cause.