Not knowing your state, I'll just give you generic advise....
There are 3 ways of looking at the commission problem. Either the agent has a no right to a commission, or s/he has a separate contract with the seller, or s/he is a 3rd party beneficiary of the sales contract. If s/he has no right to a commission, the commission dispute does not effect the sale of the house and the seller has to close on time or pay the contract penalties/damages.
If s/he has a separate contract, it has nothing to do with your purchase contract and the seller can't use the other contract as an excuse to delay performance of YOUR contract. Seller closes on time or pays damages.
If the buyer's agent is a 3rd party beneficiary of the contract, s/he has beneficial rights under the purchase contract, but is not an actual party (buyer or seller) with power to hold up the closure. Again, the agent's rights can't excuse the seller's refusal to perform his/her contractual obligations to YOU. Seller has to close on time or pay damages.
Under any scenario, whether the agent gets a commission or not is none of your affair. YOUR costs do not change whether the commission is paid or not. Tell those twit attorneys that you demand they close the sale immediately. Suggest that they have the escrow company retain the commission amount from the money they give the seller until the agent question is resolved, and proceed with closing.
Seller can't refuse to close on the house just because his/her lawyers have messed up paperwork between the seller and a 3rd party. Tell Seller that you will sue for breach of contract and damages if s/he doesn't close NOW. Be a pain in the ass and bully them into doing what you want.
Good luck,
Tracey
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This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.