Actually his proof is far better than the standard proof posted in Sales Threads on Forum Korner. Not only does his proof represent the fact that he has the Gamertag "silenced" it also proves that the account is not banned, since he can see the 'change gamertag section'. On top of all of that you can see that his avatar matches. Although anything can be faked with inspect element, this proof is pretty solid.
Also, It is the responsibility of the buyer to ensure he has the tag. The only true way to do so is to ask for a friend request. If you do not ask for a FR then the buyer is being stupid and quite frankly asking to be scammed. Also make sure to use a MM in all deals, FK provides free MM's such as myself. Also you can use Philly its only 5$, and he is by far the most trustworthy, and plus all the funds go directly to FK.