Sentence from 'Prison Break' (meaning of 'I wouldn't know?')

[Forum_Mail]

Here's a dialogue from Prison Break, episode 11.

Scofield: Still interested in getting in on PI?
Inmate: Does my mama got big breastices?
Scofield: I wouldn't know.

I don't get the last one. I've never seen such a usage of "would" before... what's the meaning of "I wouldn't know?"

[Prezbucky]

I would not know.

= I've not had the requisite experience to know what you're talking about.

= I don't know.
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Billie Jean is not my lover. Hee.