Average Salary: $46,260
Expected Lifetime Earnings: $1,931,000
Most sommeliers have a "participation" in the wine they sell. The deals work differently in any given restaurant, but the base salary itself isn't all that much—maybe $10-$15 an hour. Of course, most Somms earn a living on tips and commissions (source).
Some sommeliers simply earn a portion of the tips that equals the percentage that wine sales made up of the night's total haul. In a typical evening, say you can turn twenty tables and each table, on average, orders fifty dollars' worth of wine with an average total bill of $200.
That's a thousand bucks in wine sales out of the four grand total. The Somm would take a quarter of the total tips of the night, so his or her take would amount to about two hundred bucks.
Other restaurants will have a baseline—and the sommelier makes a larger percentage on sales above those levels.
Specifically, a restaurant might have been averaging $40,000 a month in wine sales; the sommelier makes just minimum wage(ish) up to that level—but then on every dollar above that in a month, she makes, say, 20%. If you math that out, we learn that if the sommelier can sell another $40,000 of wine, that's eight grand in her pocket.
For the operators of fine dining establishments (who just about double their money on any wine sales) (source), hiring a sommelier on some kind of commission deal is a no-brainer financial transaction. In short, you'll be paid in connection with both the quantity and quality of bottles you can hustle.