Kyuutei Kajishi no Shiawase na Nichijou: Black na Shokuba wo Tsuihou Saretaga, Ringoku de Koushaku Reijou ni Dekiaisarenagara White na Seikatsu Okuri…

[MangaDex]

 

[Darkenning]

Wow. So this what it's like to watch a complete narcissist start the process by which they destroy themselves. I mean, you hear about it happening, but you never think you'll get to sit back and watch.

 

[Toastility]

Wait... They really never checked his work? Did they only check at the beginning?

 

[Lunasol]

"Lucky guys are everywhere, and now that's me."

No, That isn't luck. You are just lazy bastard.

Fake is a hard-working yet VERY worthy blacksmith unlike you bloodsucking moron.

 

[merce6]

They're fucked up real bad

 

[Kingdo]

Wait... They really never checked his work? Did they only check at the beginning?

From the novel, they check his work when he arrives and few times after, but he was so overworked each time that he couldn't do much due to lack of sleep.
In the novel, he said that "he passed out after taking the hammer"

As for the enchantment, basically it's explained that people can see enchantment based on skill, if the work is too low or too high level it feels dizzy to look at. They obviously assume an apprentice work couldn't be better than them.