To be pleasant, efficient and tidy demonstrates your self-respect. The seasoned first-line tech or service engineer should aspire to be affable, competent, diligent, equable and tactful (look them up!). Such personal characteristics set us apart from the rabble, and (in my opinion at least) are far more important than academic qualifications (…got to keep on banging that drum!). All that should be a given, surely?
But what I was looking for in this topic was feedback about standards of dress. What is the norm these days? Personally, I favour the “designer polo shirt” approach. Practical, and smart enough for our line of work.