Surely, you can earn profit from Localbitcoins but it's not much unless you trade with a large number of Bitcoin
I think the biggest thing is risk not only of losing money but legal. Look at money laundering if you are in US. Selling on localbitcoins across state lines and not having proper paperwork can be money laundering.
I know this is a "big fish" but look at Charlie Shrem:
http://www.coindesk.com/bitcoins-first-felon-charlie-shrem-begins-2-year-sentence/ He got "aiding and abetting the operation of an unlicensed money transmitting business." for not having proper paperwork and trading btc for currency on large scale.