I don’t know about the locksmiths in your area, but the supposedly good one that my real estate agent recommended when we moved in used locksets identical to the ones from Home Depot, except he marked them up substantially. (The agent paid for the work as a gift to us, so I didnt much care.)
But having replaced the locks on our old house myself, I’m not convinced there’s much a professional (and scrupulous) locksmith could do that a handy homeowner couldn’t. Yes, you can buy cheap locksets at the local hardware store, but there are sturdier ones there, too, or online. And replacing or rekeying a lock isn’t that complicated a job.
If having a pro do it gives you peace of mind, fine. But, barring some unusual circumstances, I don’t think it’s necessary. (If a pro locksmith would like to fight my ignorance, please have at it.)
I do concur with the idea of replacing or rekeying as soon as you move in, of course.
Your key is worn. The copy works because it is not worn. The pins in your lock are made of iron or steel. Your key is made of brass. Eventually the pins will wear down your key. This is on purpose, so your key cannot be used to force the lock.
What you should have done is store the original key and use the copy, but seeing that the copy works and the original does not, you should get the lock rekeyed or replaced, then store the original and use a copy.
FYI: your key may have a number stamped on it, from 5-7 digits, depending on the number of pins in your lock. This number indicates the cuts on your key (the “bitting”). If your key has these numbers, it is the original.
Fine, I’ll wait for a pro too. But I do remember an article some years back where an ex-burglar indicated that he practiced on locks stolen from Lowes/HomeDepot. A locksmith near me did sell some brands I’d never seen in a hardware store.
But I’ll second wanting to hear from a Locksmith.
If the stored copy works, why not just make another copy of it, make sure the copy works, then store the first and use the new one? Why bother replacing everything because of one bad key? That seems like overkill. I suppose there is a chance that copying copies could eventually result in a bad copy, but as long as you save the earliest copy and use the later ones, it seems unlikely to me.
The OP says all three locks were bought together as a set, so there should have been more than one original key. Usually each lock comes with at least two keys. Have you looked around the house for other copies of the key?
And speaking as a former locksmith, as far as replacing or even fresh installing a lockset, of course there’s no expertise a locksmith has in this endeavor that any reasonably handy homeowner could not. Replacing a lockset is a fairly trivial matter of unscrewing the old one and screwing in the new one.
It’s possible a locksmith would have access to high-end locks that a consumer could not buy at a typical hardware store (e.g. Medeco, Schlage Primus), but the hardware store brands, as far as run-of-the-mill home security is concerned, are generally just fine (buy at least an ANSI Grade 2 lock).
If a burglar is going to go to the trouble of picking locks, it doesn’t really matter if he practiced on locks from Lowes, Home Depot, or the moon; a pin-tumbler lock is a pin-tumbler lock. There are certain additional features that can make a lock more difficult to pick (e.g. spool/mushroom pins, serrated pins, sidebars, wedge-shaped pins, etc.), but no lock is “unpickable.” Encountering these features could discourage a burglar, but a determined one is going to get in your house no matter what you do (there are way easier and faster ways to enter a home), but that’s probably a different discussion.