I have sent quite a few coins away to NGC for grading and had several come back with a details grade, usually hairline scratches. Sadly, in almost every case, the graders got it right. It was a lesson to me to be far more careful when buying raw coins which constitute the bulk of my purchases.
Sometimes, the thoughtful collector can take advantage of slabbing errors, which do happen, or can take advantage of those who buy the grade and not the coin. I bought a 1834 MS64 sixpence at Heritage. Per the photos, it looked like it had horrible scratches to the neck and the price reflected that. I took a chance that the scratches were on the slab and not the coin (otherwise it would/should never have got an MS64). Turned out that I was right!
I bought an MS65 1887 sixpence R/V misattributed by PCGS as a shilling with no error. Broke it out of the slab, sent it to NGC from whence it came back properly attributed and MS66. Big win!
Despite the above, and much as some of us like to deride the TPGs and their graders on here and to point out their mistakes and errors, when it comes to Details grades, the reality is that they get it right 99% of the time. And, even though the actual grade (for non-Details) is an inexact science, they generally get that more or less right too. Truth is, as collectors, we make buying mistakes and base decisions off of flattering photos too much of the time. And we don't much like it when we get it wrong. Easier to blame the TPG.
Having a few coins come back with Details has been for me an object lesson in 'Cave Emptor' and in causing me to tighten up my own grading standards. It has also emphasised the importance of trusted sources (e.g. dealers) when buying coins.