Yes B have all the rights and he can file a suit for his rights against A 

Since already sale is executed B cannot make new sale deed now. As now A is not owner no power given by him is valid for that plot.

1. POA-maker can unilaterally cancel /revoke the earlier POA by executing a new POA and THEN informing the POA holder (B). 

2. There is no legal bar to this and POA given to "C" is valid for all legal purposes.

1. Well, no sale on the basis of mere POA if the same is not given to a relative for gratuitous reasons is valid.

2. In other words if the POA is given on the garb of sale deed to avoid the payment of stamp duty is not enforceable on account of the decision of the supreme court passed in Sooraj Lamp case.

3. In other both the POA is invalid and non est in the eye of law.

The remedy of B is to file suit to get refund of his money. 

POA is with consideration(money) or without ?

If without, sale executed by C is valid. And after sale, POA to B is expired.

No sale on the basis of POA is lawful. So bot the sales have np force under the eye of law and only recourse, I may repeat, to B is to get refund of his money. 

Yes in this case for challenging the said breach you need to file a suit before appropriate civil court

A should have revoked POA given to B if he intended to execute POA in favour of C 

2) if C has executed sale  deed on basis of POA then B cannot execute any sale deed 

If sake consideration was paid by B to A then sale deed should have been executed by A in favour of B 

2) POA does not confer clear and marketable title to property 

This is what i said, if POA is with consideration and sale is illegal. Can file FIR agasint A , C and buyer.

See if there is money paid in lieu of power of attorney B can file a suit before the court for cancellation of sale and seeking specific performance of agreement if any though as per law also multiple poa can be given though if there was any consideration then B for same can contest before the court. 

- As per law, Any person who owns a property and is competent to contract can transfer it in favour of another , and can gives another individual a power of attorney (POA), further that person can sell it under this authority.

- Further, that owner can give POA to more than one person for the same transaction as well , but cannot execute separately a new POA on behalf of a new person without cancelling the first POA legally. 

- Hence, the POA given to C is not valid , and B can challenge A , and its transaction without informing B, and specially when B paid to A .

-  B should send a legal notice to A after mentioning that the transaction done with C is not having any legal value , and thereby ask for transferring the said plot in the name of B, or alternatively ask for refund the paid amount with compensation as well. A copy of the same should be forwarded to C as well.

- If no response within 15 days of time , then B should file a case for Specific performance for getting order . 

Good luck and dont forget to rating Positively. 

You was holding only the power power of attorney which was again executed in favour of see what kind of rights you have in this case you don't own the property you had some right to perform which is now performed by the C.

So far as the received after payment is concerned this has nothing to do with power of attorney this is not received in case you paid any amount against the plot to get it registered for yourself then you would have gone through the agreement to sale there are lot of problems in this case and I feel that you may not be having any ground to make objections against the transactions made by C.

1. What interest does B have in the transaction in the first place? Did A promise through an agreement to pay a sum of money in lieu of latter becoming the agent for the sale?

2. Breach of trust or contract would come into play only if B either had a right, title or interest in the property or if GPA executed by A in favour of B was coupled with interest in favour of B in which event it was irrevocable.

The POA attorney deed was not cancelled hence B is still having power to execute sale deed.

However he cannot execute any sale deed to the property which his principal is not having title anymore.

In fact the principal cannot execute another power of attorney to a third person for the same property, it may be considered as an illegal act.

A's act of giving POA deed to a third person during the subsistence of a POA in favor of original power holder is actually invalid and an illegal act especially if the same property is mentioned in the fresh power deed, without cancelling the registered power of attorney deed executed in favor of B.

Now B can file a suit to cancel the sale deed executed by another power agent for the same reason.

1. If power of attorney is executed for sale of particular property then it will be cancelled automatically after sale of that property.

2. And if POA is issued generally and not revoked by A then B can use POA for sale of other properties of A. But B cannot challenge the sale done by C.

3. In this case both POA will be considered as valid.