My low score for this episode is not due to any technical deficiencies, other than an almost complete lack of humor on a supposed comedy show. In fact, it's an almost perfect Generic Sitcom Episode; as such, it would rate a 5.0, because the highest goal of generic writing is to be average. But this simply isn't an Andy Griffith Show episode. There is absolutely nothing in it that requires or makes use of the unique characteristics of the citizens or town of Mayberry. The obvious non-North Carolinian who shows the store to Andy and the gruffly urban Ken Lynch seem deliberately included to remind us that we ain't in Mayberry in this episode.
If you allow for a generic need for extra money, virtually any sitcom character could milk a canned laugh out of running a Laundercoin. Instead or driving Munson's cab for extra cash, Archie Bunker could do it. Instead of working at a shipyard, Herman and/or Lily Munster could do it. Vinton Harper, Al Bundy, and Lucy Carmichael would all be perfect for the job. This doesn't even have to be a sitcom episode; it could exist within a drama show that uses moments of mild humor. And you still want a guy with a badge running the laundry? Bill Gannon, John Gage, or Frank Poncharello could all fill Andy's role without missing a beat.
Actually, Andy could have saved himself all the trouble of the Laundercoin just by waiting 2 weeks. Opie is 13 in this episode; his career plans shouldn't last more than a couple of weeks, and the idea that ultra-pragmatic Andy would expect anything more --and go to desperate lengths out of those expectations-- seems a little naive.