Most travel pages about Porto repeat each other. A figure appears somewhere, gets copied, and three years later it is still being quoted with nobody able to say where it came from. This page explains what this site does instead.
Primary sources, or it does not get published
Every price, opening time and duration comes from the operator that charges it or the institution that sets it, never from another guide. If a competitor publishes a number I cannot reproduce, I do not copy it: I say that they publish it and that I have not been able to verify it.
Everything checkable goes in a table, with its date
Prices, timetables and durations are things you consult, not things you read. They go in tables, and every table says which system the data came from and on what date. A figure without a date is a figure you cannot trust.
What I have not done, I say I have not done
I have not taken every tour on this site and I never will. Where a page compares tours I have not been on, it compares them on price, duration, pick up point and volume of reviews, and the author box says plainly that the comparison is not first hand. A rating of 5.0 from twelve reviews is weaker evidence than 4.8 from nine hundred, and this site explains that rather than hiding it.
Photographs
My own photographs are dated in the caption. They are evidence that I was there, not documentation of what the place is like today: ticketing systems have changed since 2017 and one of the markets has been rebuilt completely. Everything else is freely licensed photography, credited to its author and licence on the page where it appears.
Corrections
If a figure here is wrong, write to hola@diegofresno.com and it gets fixed, with a note saying what it used to say and why it was wrong.