As to the tons of articles on the interwebz from googling something....

One of the articles that's been posted and reposted is someone from consumer protection group abc takes a plug wire off of their car and goes to x number of shops to get it fixed, and then compares prices for the repair, complaining about the inequity of the quotes.

2 problems with that:

1) many shops have signs right in the window clearly stating that if they pop open the hood they're going to charge you 1 hours for diagnosis, regardless of what's required. If they're telling you this up front, how can you complain after the fact? Those advanced code readers that they're using can cost north of $15,000, and they have to pay for having it.

2) Plug wires don't just come off on their own anymore. in 1980 that little trick might have been a valid test, but not anymore.