No its not 30%. It all depends on what part of the world you are, and what method you are using. For me, I just pay around 4-5% of the bitstamp price, and it is much convenient for me, as they are protecting me with an escrow, and I can trade with reputed sellers.
Yes it is 30% except for cash at bank or wire transfers. Western Union, Moneygram, Payza, Paysafecard, PayPal, Gift Cards can be from 10% to 30%.
OKPAY, WebMoney and Perfect Money are 5% to 15% over market value. Prices are bloody terrible for all forms of payment. It's a huge RIP-OFF!
And the big sellers on localbitcoins are obviously laundering the coins they received from selling drugs, committing fraud and other criminal activities.