How we cite our quotes: (Book.Chapter.Paragraph)
Quote #1
A collier working by the piece is supposed, at Newcastle, to earn commonly about double, and in many parts of Scotland about three times the wages of common labour. (1.10.18)
In many cases, people's social class will depend on how much skill or education they have. For example, a collier (a dude who makes charcoal) with a special set of skills is more likely to make a good living than someone who can be easily swapped out for the next worker who comes along.
Quote #2
Fourthly, The wages of labour vary according to the small or great trust which must be reposed in the workmen. (1.10.19)
The amount that a person gets paid for a job will always be connected to how much responsibility that person has. If you're the one who controls the main buttons to a nuclear reactor, chances are you'll be paid more money than someone who guards the peanut butter in the break room.
Quote #3
This inequality is upon the whole, perhaps, rather advantageous than hurtful to the publick. It may somewhat degrade the profession of a publick teacher; but the cheapness of literary education is surely an advantage which greatly over-balances this trifling inconveniency. (1.10.95)
In Smith's mind, public schoolteachers probably deserve to make more money based on their skills and hard work. But he thinks that it's worthy to sacrifice their comfort for the sake of making education as affordable as possible to many young students. In this case, he's willing to sacrifice an entire class of workers to the public good.