Personally, as a collector & customer of 
Mandarake I can only say this:

I've bought 2 cels from them in the past which 
are both legit.  I've heard the rumors yes(Anyone 
else notice the crappy touch-up jobs on some of 
the line faded cels^^;?), & more.  I believe that 
you as a customer must realize that you are 
buying original artwork, & just like in the 
regular art industry...There can be a chance of 
forgery.  You as a possible client must use all 
your resources to make sure you do not buy a 
fake.  I mean...An art dealer at the Louvre isn't 
just going to accept "Monet's lost paintings" 
without checking it over first^^'!  

Mandarake has also been most friendly & helpful 
in all my dealings with them.  I mean, a dealer 
who is willing to go through thousands of cels 
they may have to find a particular scene is worth 
my time & money.  

I do want to say Thank You for bringing it to our 
attention though.  Some people in the cel 
community might not have been aware of this.  
Just remember though, a company is like an apple 
tree.  The majority of the apples are good 
apples, but there is always a few bad apples that 
can ruin your perfect crop.