since seller is residing abroad POA executed by him has to be attested by indian consulate in USA 

since POA has already been duly stamped and registered by sub registrar in Hyderabad your interests are protected even if POA is not attested by indian consulate 

Yes attesting the same by embassy is required if the gpa is signed outside India. If the same is signed in India notary or registration of that gpa is enough

If seller is not providing GPA attested at Embassy postponed the deal. Seller have to bent on your condition to complete the deal.

IS this GPA with consideration - in lieu of money ?

Well, GPA is valid.

it is mandatorily required to be attested by the Indian Consulate. This is must in order to avoid any issues later in regard to authorization..

The power of attorney deed executed by a NRI or a PIO in a foreign country is to be executed on a plain paper only and not on a Non judicial stamp paper of India, which has no jurisdiction outside India, further the said POA deed has to be attested by a Notary public of that country or by an official of the Indian embassy or high commission of that country.

The above is the law to execute the said deed.

You were informed about the law involved in this.

Will the Official at Indian consulate in US sign or attest the registered document now?

The attestation by an official at Indian consulate is to confirm that this person is a resident of that country without which a NRI cannot sell the immovable property in India through a power agent

Dear

Yes the attestation of GPA is mandatory by US consulate but If the GPA has been registered in India than he must have complied with all the conditions for GPA from an NRI. 

You can go ahead with the purchase by existing registered GPA.

Hi 

1)  GPA has to be compulsorily  attested before the Indian embassy  in a manner prescribed under section 14 of notaries act and Section 85 of Indian Evidence Act, 1872.

2) Mere registration of GPA with sub-registrar  that too after payment of stamp duty is not sufficient in the present case as identity of person executing the authority is not confirmed before the sub-registrar.

3) No further changes can be made to the GPA which is already registered by way of Attestation or apostalisation.

Hence an Effective alternative remedy can be

a) You can agree to transfer of sale consideration to the NRI  directly to his bank account in India instead of his GPA holder and

b) Also let the NRI know that you shall be  deducting TDS of 20% (if the property is at the hands of NRI for more than 2 years) or 30% (if the property is at the hands of NRI for more than 2 years) depending on date of NRI purchasing the property) .

c) All details of sale consideration and TDS deduction are to be compulsorily mentioned in sale deed 

d) In case the NRI is claiming for TDS to be deducted based on Capital gains and Not on Sale consideration, he has to provide exemption certificate from Income Tax Department prior to you paying the sale consideration to him.

4) Since you shall be directly remitting the sale consideration to the Indian bank account of NRI Seller and also will be deducting TDS in accordance to Section 195 of Income Tax Account and also mentioning these details in the sale deed,  it is the safest way to get the sale consideration done and also to get the sale deed registered through the GPA. 

5) So legally if the monies are transferred to his bank account and  TDS deducted with the consent of NRI and remitted in to the government treasury in format prescribed and sale deed executed by his GPA holder, then NRI cannot renege on the sale deed.

6) Please ensure to collect the original GPA from the GPA Holder at the time of execution of sale deed.

POST SCRIPT: 

a) Please be aware that under Income tax , there is a separate procedure for TDS if you are purchasing a property from NRI (Please refer to Section 195 and 203 A of Income tax Act).

b) Please be aware that it is the buyer's responsibility to deduct tax at the rate prescribed u/s195 of I.T act, 

Hope this information is useful