I resisted guided anything for years, on the general principle that I would rather work things out myself. Then I had one day with somebody genuinely good and revised the position entirely.
The difference between a good guide and a poor one is enormous and it is identifiable in advance more often than you would think.
What the poor ones do
Recitation. Dates, names, dimensions, the number of steps, delivered in the same order to every group, in a rhythm that suggests it has been said several thousand times.
All of it is available in any guidebook and none of it is retained by anybody.
The other failure mode is the route march. A fixed sequence of locations with a fixed duration at each, driven by the schedule rather than by what the group is interested in.
Both are recognisable within about ten minutes and neither is fixable from inside the group.
What the good ones do
They tell you what things meant to the people who made them, which is a different category of information from what things are.
The best guide I have had spent twenty minutes on a doorway. Not on its architecture but on who used it, who was not allowed to, what that arrangement said about the household, and how it changed when the law changed.
I remember that doorway. I do not remember any of the buildings I was told the dates of.
They also answer questions properly, including saying that they do not know, which is a strong signal. Somebody who has an answer for everything is producing answers rather than having them.
They have a point of view
The thing that most distinguishes the good ones, and the thing that makes some people uncomfortable.
Places have contested histories. A guide with a position on that — who says what the disagreement is, and where they stand, and what others argue — is giving you something you cannot get from a book that has been edited toward neutrality.
The alternative is a smoothed narrative in which nothing is disputed and nobody did anything wrong, which is not history.
What you want is somebody who tells you it is contested rather than somebody who presents one side as settled.
How to find them
Specialist tours over general ones. Somebody who runs a walk about one subject — food, a period, an industry, a neighbourhood, architecture — is generally interested in that subject rather than employed to describe a city.
Small groups. Above about ten people, questions stop happening and the guide reverts to broadcasting.
Individual operators over agencies, because you are booking a person rather than a slot.
And read the reviews for what people mention. Reviews of good guides name them and describe specific things they said. Reviews of poor ones describe the itinerary.
Licensed and unlicensed
Worth knowing that in many places official guiding requires a licence, involving examination and sometimes restricting who may guide inside particular sites.
Licensed guides are reliably competent and occasionally constrained by an approved narrative.
Unlicensed guides vary enormously and include both the worst and some of the best. In some places using one inside a protected site creates problems for them rather than for you, which is worth being aware of.
My own approach is licensed for anything inside major sites and whoever seems most interesting for anything outside them.
The free walking tour model
Widespread now and worth understanding before joining one.
They are not free. The guide is paid by tips, frequently pays the operator a fee per participant, and can lose money on a group that does not tip.
Which shapes the product. The tours are entertaining, broad, and structured to build goodwill toward the end, and they frequently include a pitch for a paid tour.
They are a decent orientation on a first day and they are not the same thing as a specialist guide. Paying the guide properly at the end is not optional in any moral sense.
What I book now
One thing, early in a trip, with somebody who knows one subject well.
Not an overview tour, which duplicates what I can read, but something specific — a food walk, a neighbourhood, a period, a building.
The reason to do it early is that a good guide changes how you see everything for the rest of the trip. The questions they raise are what you spend the following days noticing.
And I ask, at the end, what they would do with three more days in their own city. That answer has been worth more than the tour on several occasions.
Paying properly
Worth stating since it varies and people get it wrong in both directions.
Guiding is skilled work involving substantial preparation, and rates vary enormously by country. A private guide for a day in some places costs less than a restaurant meal in others.
Where the rate seems very low relative to the skill involved, it usually is, and tipping is part of how the work is actually paid for.
Where you have had a genuinely good day, saying so in a review by name is worth more to an independent guide than the tip, because it is what brings the next booking.