Following is Bermuda stamp issued in 1942 with 10 shilling value of King George VI.
To me it look Genuine in all respect.
But if seller did not mention it I will not notice it's forgery stamp or not real stamps.
I can even buy this stamp and sell it as genuine and wait for some one to buy or do some fake buying with my other id (cancel bid after 10-15 days as non paying buyer or mutual agreement so I don't have to pay commission) so other collectors will think it's genuine and stamp price is appreciate.!!!
On top of that I can make my own Expert certificate in order to make it more genuine. Don't you think it's possible.
Click following link to see what is expertising certificate and you will get idea.