As I read the description, this is not so much 
a "sketch" as an original watercolor art work by 
a highly respected manga illustrator.  To a CCS 
collector like me, this would be like seeing one 
of the original CLAMP illustrations in "The Art 
of Cardcaptor Sakura" coming up for auction.  I 
wouldn't bid this much (mainly because I'd have 
to sell my house to do it) but I'd certainly 
expect to see the winning price go well into the 
thousands of dollars. 

Add the possibility that the art work might be 
hentai, and the $100K price seems understandable. 
Perhaps ambitious, but predictable. How much are 
the original watercolor illustrations done by 
the "Four Old Men" of the Disney Studio going for 
these days?  I'd assume $100K plus plus?

As for typing in random numbers, I doubt it, 
since the auction was contested, and the 
underbidder would have to type in the number just 
below the "random" number, which could hardly be 
done at random.