step,rule,n_before,n_after,n_removed,rationale
1,parse with CSV quoting; require exactly 5 fields,1200,1164,36,lines with wrong field count are garbled and cannot be read unambiguously
2,require valid formats: sale_id S+5 digits; known municipality; ISO date; positive integer price (plain or strict thousands-separated); positive numeric area,1164,1164,0,fields not unambiguously readable
3,exclude duplicated sale_id (all copies),1164,1164,0,sale_id must be unique