Sometimes you need people on site in Germany to take care of your business. If these people live in Germany they will be liable to German social security and they will have to pay taxes in Germany.
a. Social Security
The social security rate in Germany is about 40%. Half of it has to be paid by the employer and the other half by the employee. The standard way is that the employer withholds the 20% of the employee, adds his 20% and transfers the 40% to the health insurance of the employee. This health insurance will forward the other parts (statutory pensions, unemployment insurance) to the other authorities.
In order to avoid this procedure you can also pay out your 20% to the employee and let the employee add his 20% and transfer the total of 40% to his health insurance. This way you would not have direct banking contact to the health insurance. However, it is important for you to know, that you still would be liable for the payments. So you need to be sure that the employee forwards your money. This is a difference to the wage tax, where you are not liable if you do not have a permanent establishment in Germany.
b. Wage Tax
Usually, the employer would withhold the wage tax and would transfer it to the account of the tax office. Since you would not have a permanent establishment in Germany you would not be the tax responsible person. Instead, you pay out the wage tax to the employee. The employee will inform his local tax office that he has German income. Afterwards, the tax office will send him a prepayment assessment with the estimated amount of taxes which have to be paid. The employee will pay this quarterly and in the total it will be net the same as if you as his employer would have withheld the taxes.