Property related VAT/ST payments what to do

Hi, i recently purchased an apartment and since i paid in full by cash - I was told VAT and ST not applicable. At the time of sale deed registration, the builder's lawyer said it is not possible to show entire amount as cash or it will impact the builder financially and asked to provide them with a few cheque leaf numbers and bank branch name so they can show some amounts paid by cheque but i flatly refused. So, they added a clause in my sale deed that states I have not paid VAT/ST and i signed it becase on asking if there would be legal/IT implications, they said that it was not my responsibility to pay VAT/ST rather the builder. On checking with another lawyer, i got to know that if govt. comes checking i will have to pay VAT/ST if builder refuses. Just here to check for additional opinions. Thanks!