step,rule,n_before,n_after,n_removed,rationale
1,keep lines with exactly 5 CSV fields and sale_id matching S+5 digits,1200,1164,36,garbled/corrupted lines cannot be read unambiguously; not reconstructed
2,"keep rows whose municipality, ISO date, price and area all parse",1164,1164,0,fields must be readable unambiguously
3,drop rows with duplicated sale_id,1164,1164,0,sale_id must be unique