Anyone that has any doubts probably should take their frame to a mechanic they trust or a framebuilder. I would never criticize someone for doing that. I still remember they guy who said he was going to build his own wheel, and asserted that he was qualified due to being a graduate student in Mechanical Engineering. I told him I was an undergrad mechanical engineering student and that he would be back. He was.

The other reason you want to do that is to get them to make sure the dropouts are parallel and that the derailleur hanger is coplaner with the wheel. I was going to get the tool to check the hangar, but it costs $75, which I thought was about $50 too much.