If you have an agreement with the agent that is exclusive, you have to pay commission. If you were unhappy with their service, you'd need to talk to them about cancelling.
Also remember that finding the buyer is only the first phase of the real estate transaction. The second phase is where it all falls apart. Someone needs to negotiate terms, buyer loan issues, inspection results, title, insurance issues, repairs, etc.
If you had bites, but no offers, it means your home was either overpriced or not up to the condition/amenties of competing homes. If people are looking, but buying somewhere else, you should have been given feedback from the buyer agents and shown new market stats.