Erase ink smudges, getting more shady (8)

I believe the answer is:

sneakier

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'more shady' is the definition.
Both the definition and answer are comparative adjectives.
Perhaps there's a link between them I don't understand?

'erase ink smudges' is the wordplay.
'erase ink' can be anagrammed to 'SNEAKIER'.
Though, I am unsure how this is indicated.

'getting' is the link.

Can you help me to learn more?

(Another definition for sneakier that I've seen is " More sly".)

I've seen this clue in The Telegraph.

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