I recall years ago my high school shop/mechanics teacher telling us that 80-90% of the successful fix-it job was using the right tools. The rest was reading and understanding the service/repair manual.
Paying a pro is all well and good but finding a good competent marine electritian can be tough. I have talked to several people who sell marineelectrical items, and repeatedly they have told me there is almost noboby in the area they trust to do wiring.
They tell me there is no reliable credentials it's mostly the expirience yard mechanic that also does some electric and some of that is clearly not done to abyc or any other marine standard.
I don't know first hand if they are right about the general state but I have seen "pro's" do some pretty bad work. That is why I go educated to do my own or at least know enough to recognize bad work.