The mission of customs control units includes the duty and the authorisation to carry out inspections on the borders and within the national territory in order to ensure that the obligation to declare is being observed.
Accordingly, your means of transport and luggage can be inspected. If there is a reasonable suspicion that you are carrying cash or equivalent means of payment under your clothing, the customs officials are also authorised to search you.
To allay any suspicion of money laundering or financing a terrorist organisation it is advisable that you carry documents that show the owner, the provenance, and the intended use of the cash or equivalent means of payment.