If done well, it is not quite as obvious as you're making it out to be, and no... this is not an assumption on my part. With paying close attention, yes... but again the fact is that an unfortunate number of people do not do so, and is why the scam I am aware of worked. For each person that pays close attention, is knowledgeable about, and focuses on the coin along with minor details, there is at least another who is and/or does not, and therein lies the danger of such things. This should be low on the realistic concern scale, yes, this doesn't mean one still shouldn't be aware and/or pay attention, especially when/if in certain buying situations. What's the old saying.... "an ounce of prevention is worth a pound of cure"? As for how it is done, it's not completely by chance; the right pressure applied "correctly" can (not will) break the seal. The exact technique escapes me, but I have seen the results and can personally testify that it, in fact, can be done.
I think that's where the difference lies, whether or not people actually pay attention. It doesn't mean people need to be paranoid but a basic check or logic test of whether everything matches up doesn't seem unreasonable to expect people to do able to do. Lack of attention is really one of the major reasons why those types of fake scams can be successful. With that said I do think it would be in NGCs best interest in being a little more proactive with staying ahead of the curve and doing a slab overhaul
You can usually get an image from pulled listings with an item number here, http://www.coincommunity.com/ebay_tools/get-large-image.asp
GoldFinger: <<When you hear these guys at PCGS, NGC, and CAC having to look at 300-500 coins a day, that's ridiculous. That averages out to 2 minutes TOPS and probably as little as 30-45 seconds on a busy day. That's too little time to look at a coin, grade it, give it a 2nd look, AND look for fraud. It's ridiculous. >> Perhaps each grader evaluates 800 to 1250 a day at PCGS. One former NGC grader told me that he graded as many as 1500 coins in one day. This article, which includes discussions of grading speed and accuracy, was the winner of an award from the NLG: How will Coin Collectors Interpret Certified Coin Grades in the Future? GoldFinger: <<Coin doctoring was another problem.... Laura Sperber was on that for a while. TPGs knew who was doctoring and sometimes didn't act. >> Laura made a lot of noise, much of which was beneficial, from 2007 to 2009. I have been "on that" for years, since 2010! The Formal Introduction of the PCGS 'Coin Sniffer' at the PCGS Luncheon Defining Coin Doctoring and Dipping, Additions to the PCGS Lawsuit Against Alleged Coin Doctors – 09/08/10
One popped up in the news today! One that was stolen in 1955! Treasure is still out there! http://www.foxnews.com/us/2016/04/17/inverted-jenny-stamp-stolen-in-1955-resurfaces.html