Haven't tried localbitcoins yet, but heard that a lot of scams happening there. Even with a cash deposit you can get scammed. They place an add somewhere that they sell something (a car, a horse, a cat, a house, you name it), then will direct a buyer to pay into your account. Even if it is a cash deposit and cannot be cancelled, the scammed buyer will surely report it to the police. So, yeah, such buyers with urgent deals and tons of cash sound fishy.