いいんすか is a slang,which is used by Japanese men only.
For example, it is often used by between "先輩" and "後輩" whereas you should never use it in a formal setting.
It is always safe to use "いいんですか"
October 24, 2012
"いいんすか”is kind of word use in Young people in Japan. Just between friend to friend should be. You are better remenbering "いいのですか？ . " いいんですか”also use for younger young person to elder young person just for acknowlage.
October 22, 2012
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Chinese (Mandarin), Chinese (Cantonese), English, Japanese