Hiya jaycroft, et al. First time / long time, here. It sounds like you're already taken care of, but I hope this will benefit /someone/ reading through here. Iofd, I am a card-carrying ALoA member and professional locksmith.
The Associated Locksmiths of America (ALoA) [0] has its own search tool [1]. Of course, the same rules apply as everywhere. Not all good locksmiths are members, and not all members are good locksmiths. But, personally, I'll take the word of a trade organization over that of an advertiser any day. The real tragedy here is that both google and yelp apparently missed the opportunity to serve up a tool like this, in favor of (I'm guessing here) whoever bought the most expensive SEO package.
To answer your question: In my experience, yelp is dealing with this by being a smaller service, in every sense.
Google has, by making itself the de faco choice for each and every mode of search, become a "bucket of crabs" [2][3]. As such, it as an environment is selecting for that crab who can best pull down the other crabs, and not the "tastiest" or whatever.
That said, I can't think of anyone, off the top of my head, who puts any money into yelp. Where I live, it simply isn't popular. It's not a part of the culture, the same way that google is, and so is not as attractive to interlopers, "puppy mill"-style franchises, etc. I believe you're getting better results simply because it's too small a bucket for bad-ish actors to see it as a viable feeding target.
Back to the trades: Imho, screw search engines at large - even ALoA's. Ask your friends for recommendations. Don't have any friends? Call up your favorite cafe, and ask them who they use. Even if their tradesmen work strictly in the commercial space, and you're looking for someone to do some residential work, they /really should/ be willing to recommend another tradesman. One doesn't work in the trades for very long, without being exposed to the other players in one's area.
Lastly, I beg you: if you've found a tradesman who treated you well at a fair price - evangelize on their behalf. Tell your friends and family. Ask that locksmith for a dozen business cards. Most of us will knock a few bucks off of a service call if we were recommended by word-of-mouth. Not everything needs to be an on-line affair.
[0] - https://www.aloa.org/index.html
[1] - https://www.findalocksmith.com/
[2] - https://en.wikipedia.org/wiki/Crab_mentality
[3] - The only entity that wins, in this scenario, is the cat who owns the bucket... I know a number of very good tradesmen who feel like they need to spend very big money on SEO and advertising just to come out one index-position ahead of their competition. If the numbers -one and -two position, on google specifically in my area, would put aside what I call their "advertising cold war," they could both afford to take a very nice holiday every year. Sadly, they choose to subsidize some advertiser's very nice holiday. So goes the world.
edit: formatting...