One technique used in Sonnet 130 is hyperbole, because the speaker exaggerates his love’s weaknesses rather than her strength.
Shakespeare plays on the fact that most sonnets decorate the lover with hyperbolic praise. Hyperbole is exaggeration. He decides to take the similes and metaphors in the other direction, instead explaining how his love is NOT more beautiful than the other.
My mistress' eyes are nothing like the sun;
Coral is far more red than her lips' red;
Instead of saying her eyes are like the sun, and her lips as red as coral, he says the opposite. At the end of the sonnet he explains that this means his love is truer, because he can see her shortcomings and still love her.
"Comparison" is the main issue focused on the poem since this is a harsh critisism of the previous era. Shakespeare doesnt cling to the concept of exxagerrating woman's beauty instead he mocks at such petrachan works. In fact he uses the images of which the pertachan poets praised their women's beauty and claims his woman is not so. At first the poem appears to comdemn the negativity of the woman's beauty but later on (in the final couplet) It is made awared that the poet's deep and rare love is not based on appearence.
Contrast is a main technique focused throughout the poem. (with exaggeration)