About 8 percent of cases concerning purchase contracts that have been handled by the Beijing Haidian District People's Court in the past three years involved consumers, a judge from the court said while urging consumers to be more careful.

In such disputes, "people often initiate lawsuits against service providers, especially health or fitness centers, for irregularities or for defaulting on the implementation of service contracts," Judge Chen Changyi said at a news conference on Monday.

For example, a resident surnamed Kang registered at a fitness center in April 2018. Kang paid 5,000 yuan ($762) in membership fees and bought a swimming card, according to a case disclosed by the court.

According to Kang's contract, the center was supposed to open for business in May that year, but it did not. Kang eventually got a refund only after taking the center to court.

The court found that contract between Kang and the center was real and effective and that Kang had the right to terminate it because the center didn't provide the service it had promised to.

Considering that more and more people are becoming fond of bodybuilding to keep fit and healthy these days, Chen suggested consumers pay more attention to so-called membership systems in such institutions.

"Many fitness centers often attract people by selling classes at a very preferential price, or telling people they can get a discount on classes after buying memberships, which are sometimes risky," he said.

He also said consumers should buy short-term class cards in gyms instead of long-term ones and take the initiative to preserve evidence, such as pay receipts.