Like any industry there are a some really good smiths and some really bad gun plumbers.
Thought I'd share some personal experiences - intent is not to get into a name and shame libel case.
A guy at the club bought a second hand Tikka M595 with a .30-06 rebarrel by a fairly popular "smith".
On the first day out with the rifle the owner used some loads that came with it - not something I'm keen on.
First round ok, second round the case head separated. Not funny but no injury.
First assumption was a bodged hot load with some old corroded brass. The unfired had corrosion spots and I pulled one of them - it was a compressed load which while not truly indicative of hot is not a comforting sign.
I loaded the second batch with him, N140, 155gr bullet all well within limits with new, fully prepped brass. First round jammed after firing.
When we eventually got it out the webbing was visibly larger circumference than the case wall.
I insisted it get it's headspace checked by someone other than builder.
Turns out the bolt face was quite some ways from the end of the chamber meaning a completely unsupported stretch of brass.
The oversize headspace gauge closed comfortably.
Second experience is a rifle where the barrel unscrewed while I was taking the mod off.
Now I fancy myself as having strong hands but that shouldn't happen.