According to the policy I understand, the deposit of stalls in university canteens is not refundable, which may be illegal in some places. Specific regulations will vary from region to region, and you can refer to relevant local laws, regulations or policy documents.

In most places, merchants are required to clearly inform the purpose of the deposit and the refund conditions when collecting the deposit, and indicate the relevant terms in the contract or receipt. If the canteen stalls fail to express or return the deposit in time according to the agreed conditions when collecting the deposit, it may constitute an illegal act.

However, it should be noted that the laws and regulations in each place are different, and the specific situation may be bound by the policies of universities or schools. Therefore, I suggest consulting relevant local laws and regulations, school regulations and relevant consumer rights protection regulations.

If you have any questions about the specific situation or need further consultation, please consult the relevant local departments or legal institutions to get more accurate and specific answers.