I would probably start by taking that side plate off it looks like it could be a mortise cylinder. If that’s the case there should be a set screw underneath that plate that would allow you to unscrew the cylinder for servicing.. EDIT: I just examine the pictures a little bit more closely could be a simple as a Kik cylinder under the outside plate.
But yeah I would get a second opinion. Form a different locksmith.. 100% rekeyable.
I am trying to adapt an existing smart lock with this type of deadbolt for an sliding door I have. When I do my searches this type of lock never shows up and on Alibaba.com this one shows as bathroom sliding door deadbolt, which is not really what it is. This one would be great, except for the screw holes not being offset as many of the standard deadbolts mechanism.