Replacing an Instrument Panel

My fiance’s 96 Honda Civic recently had its speedometer stuck at about 20. We took it to my mechanic who said that the instrument cluster needed to be replaced, and said that they could get one at the scrapyard and do it for $300. We then called her family mechanic who said that it was probably just a bad connection, but after he looked at the car he agreed that the instrument panel needed to be replaced. However, he said that it would be illegal for him to do so and that we must go to a honda dealer. We did, and they replaced it to the tune of $375. The new odometer read 000000, and they put a sticker on the door that explained the discrepancy. Which mechanic was correct? (The state is Tennessee) Could my mechanic have legally fixed the car? Thanks!

I would call the state DMV and ask them what the rules are, this probably comes up frequently.

I have personally replaced speedometers/odometers in my cars (including resetting mechanical odometers to reflect the correct mileage for the car). I don’t really know/care if it is legal in my state.

This may vary by state so I agree about calling the local DMV.
I’ve repaired and changed a lot of them out. The only stipulation was that the odometer change had to be noted on the door jam. This was usually done with a tag or by engraving.
As far as I know it is not illegal for a mechanic to change out an instrument cluster or speedometer head.