You can try that but it is not that easy. If you mark the value of a rare Mosaic 5CD set as "$30 (used CDs)" the customs may not notice the "fraud", but in doubt they can always ask the receipient for a proof of the value, which will then show that the set was auctioned for $250 ...
Not necessarily. Moral issues aside, it shouldn't be difficult to load the auction page source code into an html editor, exchange the actual item number for an item number no longer in the ebay database, alter the price...