Paranoia is a good thing for sure when it comes to money/worth-related things BUT why don't revert to something which works quite well in real life/with fiat money: contracts/agreements/treaties (whatever you'd like to call them). At least when it comes to a larger transfer of money/btc this could come in handy. This even works within the digital world. Set up a contract both parties agree on and let both contractual partners sign this contract with a class II certificate issued by an approved CA. In Germany there are even offically accredited CAs (accredited by the "Bundesnetzagentur" (lit.: Federal Network Agency)) (accredited CAs). One of the accredited CAs is the "Bundesdruckerei" (lit. Federal print office). Its subsidiary D-TRUST offers class II certificates for personal use for 83,19 Euros (link) which are valid for two years. Tractis will help to find a CA near you :-)