Once a season (in the fall before storing) you have it professionally
sharpened for about 25-30$ US it takes about 45 min of labor on
machines costing $10,000 or more.
In between you back lap the blades by using either abrasive strips or
lapping compound while spinning the reel in reverse.

I gave away the machines to sharpen reels because my customers had
unreasonable expectations regarding time and cost and don't care for
their equipment properly.