PSU is most likely going to be the hottest part in the computer, so I'd be having it blowing air out the back of the case.
Either way will probably be ok, but as its also the highest vent in the case, having it blowing IN, isn't going to work so well when convection comes into play.
Your right. Electronics always will get very hot. The heat shortens electronic components over time.
Other thoughts:
Hand soldering should be easy to learn. There is a lot of tutorials on youtube how to do that.
I don't understand why the guy didn't do it the way you wanted. Customer is always right.
