So if i buy from a reseller and i doubt it will happen but what if they send me a key that was used? Can the other owner of the key view any details about my pc. I heard the Avast Premier has a remote pc feature is this true? would the other own be able to remote my pc. Is there any risks if i got a used key. by accident.
An official Avast reseller won’t provide a used key.
Besides what Asyn said, the remote support/control feature has been removed several months ago.
Chance of getting a used key from a official reseller is likely smaller than you winning the main price in a lottery 
License file/activation code is generated for the user that is buying the subscription and only send (and connected) to the buyers email.
The big key (excuse the pun) if an Official Avast Reseller, listed on the avast website, then the risk is extremely small as both Asyn and Eddy stated.
That said, you would be backed up by avast, the chance of the reseller being removed from the list and issue of a good license.