Penny Black - GB 1840 stamps of Queen Victoria - QV stamp

Recently I saw  Penny Black - GB 1840 stamps of Queen Victoria - QV stamp sold for $7100 by eBay seller "collectstamps" from UK.

But stamp location is USA.!!

So which country will get all the taxes such as Capital Gain Tax, State Sales Tax or VAT ?

USA or UK ?

If it is bought by UK buyer then he/she don't have to pay VAT.!!!

Also not sure how Capital Gain Tax rules will apply.!!

Now if you look at there were 61 bids for this auction from 15 bidders.!!

Also it was sold 1/4 price of catalog value.!!

http://gandhistampsclub.blogspot.com/2016/02/great-britain-gb-stamp-collection.html

But what are chance of this stamp as FORGERY ?

What are chance of this  SHILL bidding or FAKE bidding were buyer  wins auction and don't pay.

What are chance of increasing the price were bidders increase price so there stamp collection price increases.

What are chance of SHILL bidding where some relatives or philatelic friends or with buyer's other id bidded on this item to increase price or might win the auction.

What are chance of seller cancelling the eBay transaction ?

Do anyone collect stamps ?

Thanks
GSC.