First of all, look at the use period and remarks on the buffet coupon, whether it is within the time limit, whether there are remarks, and if the price increases, it is necessary to make up the difference.

Secondly, if the buffet coupon is used within the validity period and there is no special indication on the coupon, it is a breach of contract for the restaurant to ask for the difference.

There is no specific provision for this, which is based on the relevant theory of contract law: buffet coupons are an expected consumption behavior. After customers buy buffet coupons, the restaurant promises to provide corresponding services, so the contractual relationship between the two parties is formed. If the restaurant fails to provide corresponding services in violation of the contract, it shall be liable for breach of contract.

The following treatment methods can be adopted: refund, request for service commitment, and complaint handling with the consumer association of the industrial and commercial department.