If your buyer's agency agreement guarantees the agent a certain commission and the house you purchase does not meet or exceed that commission then you may have to pay the difference.
For instance, if the buyer agency guarantees the agent a 3% commission and you purchase a house in which the seller is giving a 2.5% commission to the buyer's agent then the agent can possibly make you pay the 0.5% difference.
Watch what you sign and possibly seek legal advice if needed.
Long & Foster Real Estate, Inc
Lehigh Valley Office, PA
You have a lot of "what ifs" in your question.
I would suggest that you go over each and every question with your agent prior to you signing anything.
And if you are still wary about what you are signing, I would consider consulting an attorney.