Yes, but you can ask the right questions. Is the rotor really a 42 deg? is the coil rewound and what method and what sealer used for sealing it? Is after sealing, then the rotor balance checked and adjusted?
You can ask the particular numbers of the 2 coils resistance and isolation value, ask about the safetygap gap and what manufacturer and type of condenser used.
And what magnetizer gear used, it has to be strong enough. Most good ones are large and heavy. Two things go into design of an electromagnet. The number of amp-turns (AT) and the magnetic permeability of the pole pieces. I don't go into the permeability here. 6000 Ampere turns or better is about what is required to saturate an ordinary magneto magnet.
What test method used to check the finished result? Is it durance tested in a hot state? What spread in ignition timing does it have when running, it should be within a couple of degrees at the max. And you can ask what particular things you should check in the future, to know wear limits and things good to know when a service or refurbish is needed.
If they can answer all that with numbers and confidence, then I would trust them, at least a bit further than I can throw a stone...But I still would check it over, all screws and nuts. And the shaft in-and-out play. It should be zero or very close to zero.
