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
I am sure you can find a reputable seller who can make the exchange easy on you. However, you should not send large amounts of cash through the mail...
First, you should trade sensibly by choosing reputable exchangers.
Second, if the seller lies and you protest, then basically the exchange support cannot rule against you.
Third, for cash in mail it is highly suggested that you require video evidence of the pick up of the package, opening of package, counting of the money, and validating the legitimacy of the notes. How will somebody fake the pickup of a package of cash at USPS? If you also make a coinvincing video then support cannot rule against you.
Ask any reputable cash by mail seller for more tips.