There are also people that do cash in the mail on Localbitcoins, but they either use escrow (which requires total trust with the person doing the escrow) or you have to send the cash first and hope they send you the bitcoins later.
This is wrong; the sellers on localbitcoins use the site escrow, so you only need to trust the exchange escrow and arbitration system.
Wrong again. If you are sending cash in the mail then you need to trust the person you are buying from as there will be very little evidence for either party to give to the LBC escrow service so they can essentially rule either way