If you want to apply a respect/disrespect lens, "I could do that" is the disrespectful position.
The respectful position is "this isn't my speciality, it's yours, tell me what you need and I'll get out of the way."
"The time it would take me to acquire your skills is more valuable than what you'd charge to fix my problem" is acknowledging the plumber's value, not diminishing it.
The respectful position is "this isn't my speciality, it's yours, tell me what you need and I'll get out of the way."
"The time it would take me to acquire your skills is more valuable than what you'd charge to fix my problem" is acknowledging the plumber's value, not diminishing it.