anything wrong happens 1st person to get arrested is you, then the rest of the buyers' hope & pray that everyone is sane like you keeping track of buyer ...
on safe side you can write a letter to excise office with copies of sale & transfer deed present it to eto personally and get it received / stamped with date / time of document acceptance at eto office. those documents will be made part of the file on date of submission., after that date anything happening, will be traced to the person who purchased it from you, as per sale deed cnic & delivery letter.