If you want to go with peace of mind and avoid from troubles to arise in the future, I would sincerely suggest to ask them that if they have NOC from the concerned authorities? and especially RDA, etc. (if it comes under the jurisdiction of Rawalpindi). If YES, then ask them to show you some documentary proof, and then you may counter verify from RDA (through website, helpline, visit office, etc.) and you are safe. Otherwise, if there isn't any such thing, sell it one way or the other, and invest your hard earned money in somewhere safe housing project, which meets all the criteria and have necessary permissions, NOCs, etc.