Former practicing chiropractor here. Here are my thoughts on what has been said / asked by the OP and others.
Free dinners - one office I was with did these, and I was the speaker at most of them. We viewed it as education and marketing. Most people don't know what chiropractic is and how it may be able to help them, so we talked about that. That's the education piece. We did offer a free exam and x-rays and encouraged people to sign up. That's the marketing. Not everyone would of course, and even then not everyone showed up. But many did. I would always give a professional opinion as to what I felt they needed for their care. Occasionally I felt I couldn't help someone, and I told them that and referred them to the professional that I thought could help them.
Multiple visits for extended periods of time - It is not uncommon to require more frequent visits at the beginning of care. We are working on correcting the problem and the body can take some time to respond and begin healing. Kind of like stopping a train and reversing its direction, or the law of inertia. However, that period should not be indefinite. For the way I practiced, it may mean 3-5 times per week for 1-2 weeks depending on the level of severity or acuteness of the problem. This then would be followed by a decrease in treatment frequency over a period of time, coupled with re-evaluations until the patient reached their optimum level of improvement. Which brings up the point that not everyone can be "cured" or made to be 100%. If it has taken years to get to the point where symptoms have made you seek treatment, it may not be possible to obtain a 100% improvement due to the degenerative changes that have taken place. Or if it was an injury, there may be damage that was done that can never be made "normal" again. That does not mean that you can't become symptom free and live normally. Just like a torn ACL that is repaired - you will be able to function normally (or close to it), but it will never be the same.
As for ongoing period treatment (or maintenance care) - This is how I explained it to patients: Just like exercise and /or dieting to get into shape, lose weight, etc. - once you reach your goal, you don't just stop. If you hire a personal trainer to get you into shape, do you think he / she would tell you to quit the gym once you achieved your goals? Wouldn't they recommend still checking in with them maybe once a month or a few times a year for evaluation to see if you are still on track? You have to continue to do something to maintain your gains. Just as you should maintain your car, house, brewing equipment (had to relate it to beer somehow!), you should maintain your body. This also includes whatever routine medical exams / tests are recommended at your age. I never could understand why people thought that this was an odd concept, or that the Dr. was trying to "take your money forever". A concerned medical Dr. is going to recommend taking care of your health, so why is odd that a concerned chiropractic Dr. is recommending the same thing?
And chiropractors that claim that they can treat anything - in general I would not recommend them. Chiropractic can help a lot of things, and can help your body be more healthy, but it cannot do everything. Just as your MD can't do everything either.
And like anything else in life - one person does not speak for the whole profession. If this guy doesn't make you comfortable, then seek a second opinion. The world if full of people that aren't good at what they do. Be it an athlete, mechanic, IT person, investment banker, medical doctor or chiropractor. But there are people who are good at what they do in every profession too. Seek one of those out and don't let the bad ones spoil it for those that do it right.
I'll get off my soap box now. Hope this was helpful in some way.
