Edelbrock Cylinder Head Quality

Edelbrock Aluminium Cylinder Head Quality Issues:

Seems that it is common and good advice to get your new Edelbrock cylinder head purchases checked out by your local machinist, to check for flaws prior to installation??

I have read of issues associated with the valve guide clearances being too tight??

I have read of complaints with the valve and valve seat machining and fit up??

Are these the main/only quality issues??

Are both these issues easily fixed??

What is the problem with the valve/valve seat set up exactly, and what is the solution??

Just trying to get a better understanding.......

Many Thanks in advance for any help/feedback/comments.....