Free walking tours are a crowded business in both cities and most of them are the same lap of the same squares. Tours4Tips splits its day in two, which is the useful idea: the 10:00 tour goes to the parts of the city tourists do not reach, and the 15:00 tour does the famous things properly. Do both and you have had a full day for whatever you decide to hand over at the end.
In Valparaíso that means the hills and the murals; in Santiago, the markets, the Vega, and the historic centre. Guides are local and the pitch is explicitly to make you feel like a resident for a day rather than a visitor ticking sights.
They register with SERNATUR under the name Tours4Tips / La Bicicleta Verde. Book through the website or by WhatsApp on the number they print on their contact page.