... For those of you who hire local guides, did you use a service such as toursbylocals.com, or did you find your guide some other way? Do you think it enhanced your experience to have a local guide? ...
The only place we've been recently wherre we didn't hire a local guide is Norway, because they were hideously expensive. Recent trips to Ethiopia, East Africa, Myanmar and Vietnam -- all local guides.
Our preference is to have a guide that travels with us, like having a local nephew, niece, or uncle. We prefer older guides, too. The kids know the dates on all the paintings and the height of all the statues, but the older guides have life experience in the countries and can give us a historical and political perspective. We once had a guide in Panama who was a retired bank executive and who had testified at the Noriega trial in Florida. Fascinating guy! The best time to talk to these people is over a nice dinner; it takes a day or three for them to get us calibrated and to open up but it is worth the investment. it's not uncommon for this type of guide to invite us to his/her home for a visit or a meal.
What you get from a good nephew/niece/uncle guide simply cannot be had by driving around and looking out the car windows. You don't waste time on stupid things. You don't get lost. You don't worry about finding a good restaurant. And you learn a ton.
A distant second-best option is to have a different guide every day or two. With this approach you tend to get mostly the tourist sites and tourist facts. Much less valuable than having a local friend for the whole trip. But with planning you can steer the day guides. For example, we spotted the "Park of Fallen Heroes" in Moscow (
https://www.atlasobscura.com/places/fallen-monument-park) in a guide book and had our guide-for-the-day take us there. Fascinating place!
I have looked at toursbylocals.com but mostly to identify guides to google. I'd rather have 100% of my money go to a guide than to force him/her to pay a big commission for the business. Not fair to touorsbylocals, I know, but that is the way I feel.
How to find the guides to travel with is another whole post. It takes a fair amount of time on the internet but that is part of the fun of planning a trip.