At the interview, not only a company representative evaluates a potential employee, but also vice versa. It happens that a person is suitable for work, and they are ready to be hired, but the applicant himself was unhappy with the interview and the employer's proposal. In this case, you need to be able to politely refuse the vacancy.
Please report your refusal as early as possible. It is advisable to do this even during the interview if you have definitely decided that work in this organization is not suitable for you. If you made a decision after the interview, call the HR department and warn that you will not be able to go to work on the appointed day. It is simply impossible not to appear without warning, because the leadership is counting on you. In addition, the HR department will need additional time to find a new employee.
Don't take your refusal to work as a tragedy. Sometimes people hesitate, are afraid to communicate their decision and even work for a long time, sincerely hating the company and dreaming of leaving as soon as possible. If the working conditions do not suit you, feel free to refuse. Nothing bad will happen, the employer will simply find another employee. Adequate leadership is always sympathetic to these situations.
If possible, try to reason your refusal politely. Of course, you shouldn't tell that you don't like the HR employee or that you think the manager is not a very smart and adequate person. Refusing a job correctly will not even close your chances of trying to get a job with the same company again. The most polite and correct argument in this case is an invitation to another, more suitable position.
Try not to go into details or talk about all the events that prompted you to give up this job. Keep your conversation with your employer short. Be polite, apologize for the inconvenience and wish the other person a good day and the company prosperity. You can also express regret that you have to give up such an interesting job. Do not overdo it: your speech should not turn into a stream of flattery.