Good question. In Maine if you have a buyers agreement with a new agent, then you would go through the new agent for the house you saw last year. If you do not have a buyers agreement, you can still use the new agent, however, if the prior agent had showed you the house, he or she may claim it was a procuring cause and request a commission.
Commission is usually paid by the seller to the listing agent. The listing agent will discuss the percentage to be paid to the buyer's agent. Sometimes a buyer is asked to pay a part of the buyer agent's commission.
I hope that answers your questions. It can be confusing. If you are still not clear, please let me know and I'll try to state it a different way.
In the meantime, if you would like me to make a good referral to you in the Guilford area, please feel free to contact me at 207-615-1663. I would be happy to put you in the hands of an experienced agent who has earned an Accredited Buyer Representative designation like myself.