In some countries, you'll be approached by independent "guides" on the street - I had that experience in Parachco, Mexico, where a wonderful local toured us through guitar shops in Mexico's famous guitar capitol (a $10 tip bought us an afternoon of insider knowledge - and we bought a guitar). If you're staying in a reputable hotel abroad, the concierge will be able to hook you up with a reliable private outfitter for guided trips. I've talked with travelers who make a practice of buddying up to a taxi driver and negotiating a tour after the driver is off duty.
Your choice - solid guides with permits whom you can book for up to several days or "entrepreneurs" for an hour, a day or more with whom you can negotiate (i.e. cash on the barrelhead).
Choose your adventure!
