Unless the Chief Commissioner in sanctioning the sale otherwise directs, a purchaser of any land sold for arrears of revenue due in respect their of acquires the full proprietorship or superior or inferior proprietorship of it, as the case may be, free of all leases, liens and other incumbrances; and all grants or contracts previously made by any person other than the purchaser in respect of such land shall become void as against such purchaser. Nothing in this section shall--
         (a) affect the rights of any proprietor, superior or inferior to the defaulters, or of any malik-makbuza or occupancy-tenant, who does not derive his rights as such proprietor, malik-makbuza or tenant from express contract with such defaulters, or any person through whom they claim; or
         (b) apply to lands held under leases at fair rents for the erection thereon of dwelling-houses, places of worship or manufactories, or for working mines, minerals, coals and quarries, or for laying out and maintaining gardens and burial-grounds, or for constructing tanks and canals, so long as the lands continue to be used for the purposes specified in such leases respectively; or
         (c) deprive any defaulter whose property is sold of the rights in respect to his sir-land conferred by any law for the time being in force.
     The Chief Commissioner may, from time to time, determine what rents shall be deemed to be fair rents within the meaning of this section.