Walking tours...free or otherwise

I always look for free walking tours in any city I'm in.
In Reykjavik I used citywalk.is and had an incredible experience with a high school history teacher who really knew her stuff! She was informative, entertaining, and shared a lot about living in Iceland as a citizen. She wasn't selling another "for pay" tour...she was making money via donations. At the end most people gave here the equivalent of $10 - 20. I believe she had a small collapsible container we put our money into. For this tour you made an online reservation that took only a limited number of people.
I did another one in Copenhagen through the tourist office...again, a local guy who knew a lot about the history of the city as well as Danish culture, economy, social structure, etc. He was informative, his talk was not "canned", and I enjoyed it a lot. Same thing with the donations at the end. This tour was a just-show-up tour and we had maybe 15 people in the group.
Recently when we were in Edinburgh you just looked for a person with a giant yellow umbrella and could take a tour with them without a reservation. The tour was good and I learned a lot about the city...
For the free tours where you don't make a reservation I have never seen one that limited the group size...you just follow the guide around. If you think there are too many people you can just leave the group.
Since this is a job for many of them they will make it abundantly clear how to donate!

I think you have to look at tours as a way of being entertained for a while and gaining more information than you would gain on your own....not comparing it to a private guide. As a solo traveler, I am doing so much planning and daily traveling, that I have enough information coming at me, that I may not appreciate or take in all that a private guide can provide....certainly not for their costs. To me a free tour is a great responsibility break and if I learn something - then that is the icing on the cake.
(know that some locals overhear guides - like in Venice - and they state the information can sometimes be incorrect and straight lies at times. If it is crucial to have correct information, then double check it after the trip).
However, you are clearly researching companies that seem to want to maintain a strong reputation - most likely better than the Yellow, Red or Blue Umbrella groups.
If you aren't aware of them, there is an organization of volunteers that are meant to be ambassadors for their cities. It is the Global Greeter Program. It would be a one on one interaction for 2-3 hours and there is no tipping allowed. You meet with a local who will walk you around. Your discussion may vary depending on your interests. It isn't the same as a tour guide, but I always thought it could be a great way to get the feel of a city early in a visit. Unfortunately, I didn't get a match with my 2 Spanish cities I approached, but it doesn't mean I wouldn't give it a try.

There are also tours that aren't free, but also aren't private in most cities. These are tours with professional, well trained guides offering correct information about the history of the city and the sites you see. Cost? Usually around 12-15€. Suggested tip for the "free" tours? 10-20€.

My experience with the "free" tours has been awful. In Edinburgh, it was the Sandemann, New Europe tours. You could tell the guides there just memorize a script as there were so many groups passing by and you could hear them repeat the same sentences! The tour was boring, half the people had left by the end, and the begging for tips was annoying. The guide couldn't answer any of our questions either. They take your photo at the beginning so that the guide can be charged for each person who starts the tour. Usually between 2.50-3.50€ depending on the city.

You all know I love Frankfurt and I know the city quite well. When I went on the Free Alternative Tour here to check out what they were saying, I was appalled. For 2 hours, the guide told the group so much incorrect information about the city, I didn't know if I should laugh or cry. Most people know very little about Frankfurt, so here was a group of 25, who were being told nonsense but of course didn't know any better. As a professional courtesy, rather than write a scathing review, contacted the management and let them know that their guide really needed to visit some museums and at the very least do some studying on Wiki.

If you hang out on the Trip Advisor forums, posts are made all the time about the utter nonsense people have heard the "free" tour guides say on their tours. Their groups are huge, and if you read their reviews, make sure you read the bad ones. They are pretty enlightening as to just how awful a tour can be.

So, if you are going to tip the same amount as what a professional, high quality tour costs, why would you go on a "free" one in the first place?

We have never been disappointed with any of the free walking tours we have taken in various cities.

I tip according to the quality of the guide, but usually for a half day tour the equivalent of $20. In some cases, our guides appeared to be University students that were pickup up cash on the side without the overhead of a tour office. Our last guide was in Quebec City, Quebec and he was a retired gentlemen that just seemed to enjoy showing others his city.

Thank you, everyone, for your replies. Yes to my mind a free tour which you end up paying for in the form of tips seems like a contradiction in terms. I will do my research with even more rigour so the only tours I join are worthwhile.

I have to agree with Jo here. There are some places (like England and Paris) where you can arrange free tours by good local volunteer guides who do not want or expect tips. These people are passionate about their city and want to share it, and they may be a bit eccentric but you're going to get some good information.

But the "big" free tours are close to being scams. You're pressured/expected to tip a substantial amount but the tours are generally substandard, given by college students who are being way underpaid for their work (as the company takes a substantial cut of their "tips"). It's a bad business model and on ethical grounds alone, I reject it.

I'm not rich, and my travel style is pretty "budget" by RS standards, so when I want a walking tour I take a public tour with a reputable organization like London Walks which costs 10-15 per person, or if I'm somewhere like York where you can get a private tour at a very fair price, I'll do that, like the 28 pound tour my husband and I took with the Shadows of York tour just last Friday.

But in general I think most people on a budget in a city where private tours are expensive are better served by going to the TI or getting their Rick Steves' book and doing a self-guided tour than they are by taking a "free" tour unless again, it's by a good organization of dedicated volunteers.

It also never hurts to email a tour operator and ask if they can get you on another tour at a more reasonable price than a private tour. A lot of tour guides are self-employed and will work with customers to find a solution that works for both of them!