I'm afraid but your lawyer's advice is grossly incorrect
A search certificate is no substitution for a legal heir certificate or a letter of administration issued by the court
You would be walking on a slippery slope if you were to rely on the search certificate and proceed with the transaction
In future you may face trouble when you go to sell the flat
Specially when the buyer is financed by a bank
The bank would obviously require the heirship certificate and in absence of the same the bank would not sanction the loan of your buyer. Thus you would get stuck and your buyers profile would get restricted who would agree to buy the property on as is where is basis, however at a discounted sale price
Thus you would be losing on potential buyers and also the property would fetch you lesser price
Even if the buyer is not financed by a bank, the buyer himself would require an heirship certificate as part of his due diligence
I'm surprised that lawyers are giving erroneous advice and that too with so much confidence