Are there any legal implications when using localbitcoins.com? You can get BitCoins for under 100 bucks via CoinBase and there are people on LocalBitCoins who are advertising offers to buy BitCoin for over 100 bucks.  The spread is around $10; so I was considering arbitraging.  Are there any laws that would apply to transactions conducted through the LocalBitcoins website that I might not be aware of?  I'm thinking of a situation where a person you sell BitCoins to might, unbeknownst to you, turn around and do something illegal with them, and get caught.  Would the seller of those coins some how be in the wrong in the eyes of the law?

Edit: I'm looking specifically for applicable US laws it would probably have to be several thousand bucks a week to be worth the time.
I'm not a lawyer. In the U.S., the lack of mens rea in your example would not cause you to have violated any laws.  As a person selling your coins, it is not your responsibility to determine your buyer's intentions.  

Of course, this is not quite so simple.  Money transmitters have regulations that include AML/KYC (know your customer) requirements which might be a factor here.   FinCEN has asserted that the conversion of bitcoins to and from cash (or other substitutes for value) is transmission of money.  So if you are engaged in trading as a business (i.e., not as an "infrequent" trader) you would likely be expected to be registered as a money service business (MSB), be licensed as a money transmitter and follow the AML/KYC requirements when conducting those trades.   Those requirements would involve gathering identity in certain instances, keeping records (for five years), and reporting suspicious activity.

Now, whether law enforcement will pursue a trader for trading without registering or following AML/KYC is unknown.  There are multiple individual traders whose banks have taken action to shut down service to their customers whose banking activity might be linked to providing Bitcoin exchange services.

So regardless of whether there is legal risk, there are other hurdles when engaging in trading to consider.