Judge, after tip-off, goes by — heading for Specsavers? (6)

I believe the answer is:

assess

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'judge' is the definition.
(assessing is a kind of judging)

I cannot understand how the rest of the clue works.

(Other definitions for assess that I've seen before include "Rate, evaluate" , "Remedy for all ills" , "Weigh up, estimate value" , "Put a value on" , "Estimate, gauge" .)

I've seen this clue in The Guardian.

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