240v 30amp recepticle fries another one!

My friend just brought home a new travel trailer and plugged it into his 30a rv receptacle mounted outside his garage. You guessed it, 240 volts instead of 120. He got his electrician out to check the damages and he took full responsibility. He had one of his employees wire the receptacle and was amazed that the employee could have wired it that way. At least the electrician is paying for the damages to converter, microwave, tv etc.
Dave