I am sorry to hear that your calls are not getting returned. Do you have a writen Buyer-Broker agreement with this agent? If so you may be wedded to your agent. If not I would put them on notice to withdraw your offer (in writing) and them secure a Realtor to represent you. Good luck.
The first thing that I need to ask you is do you have a Buyer's Broker Agreement with this agent?? if so, then you can not switch agents because you have a legal contract with that agent and you will owe him a commission if you buy a house. If you did not sign any agreement with that agent, try one more call and leave a message that informs him that you want a call back within 24 hrs or you will be going to another agent... I think that would only be fair, don't you? Just in case there were some circumstances that were not relayed to you about the seller's situation. If your call does not get returned within 24 hrs, go seek another agent and be upfront about the first agent. Tell your new agent that you want to make an offer on a house that is off the market and he will check it out to see if the homeowner has any legal commitment to the previous listing agent. If there is no legal commitment he will be able to handle your offer without a problem.
As far as choosing an agent, go with a recommendation from your family or friends that have recently used an agent they were happy with then interview that agent to make sure that there is no personality clash and that you feel good about working with him... I hope that helps you some and I wish you luck...
Joe Ski Joseph Zakowski, Holiday Florida - Future Home Realty