He probably didn't know she was underaged. It depends on how the "sting" went down.
Back in the day, they'd just send a minor into the store and have them try to buy smokes. If they could succeed, they busted you. Of course, they'd send in the most adult looking 17.9 year old they could find, but that was all fair, right?
If they got you that way, your best bet is to go to court, plead your case, and ask for a reduced fine. Obtain a picture of the minor used to sting you. It'll go a huge way towards getting a judge to go light on you if the minor in question looks like he's 40. Believe it or not, sometimes these cops will actually dye the minor's hair to make it look like they've got some grey in there. There are some situations where you can call entrapment, or at least call into question the culpability you had. If the judge thinks that it was unreasonable for you to be able to tell that someone was a minor, he'll be much more likely to let you off, or reduce the fine.
Now. If the girl came up to you and told you she was a minor, and then asked you to sell to her anyway (another better method of sting IMO). You're pretty much screwed in that case. You knew she was underaged. You sold anyway. Pay the fine. Be more careful next time. There's pretty much no way out of this one.
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King Nobby wrote:
More words please