Of course you do not have to accept the offer. However, do not refuse it rudely, without serious reasons. This is especially true if you use the services of a recruitment agency. A representative of the agency has already devoted much time to you and pre-selected job offers that might interest you. Legitimate reasons for refusing such offers include another offer or disagreement with the proposed working conditions.
Finally one more recommendation for cooperating with a recruitment agency. Do not call the agency every day to ask when they will find you a job. They know about you and are working on it.
Can you think of another mistake job applicants should be aware of?
-kk-