With the permit, Zhang cleared her sitting room to trade. Two years later, she halted the business in the end of 1982 following her marriage to Yu Xinguo, preparing for the birth of her baby.

However, it was beyond her imagination that the permit would have historical value. In 2013, it was categorized as a movable cultural relic by a national survey working group looking at such items.

Movable cultural relics are typically objects dating from various historical periods, such as works of art, documents, manuscripts and books.

In 1985, Zhang's family moved into a new apartment of around 40 square meters, which was purchased with 9,000 yuan ($1,300) borrowed from relatives and friends. The payment was 180 times that of the monthly salary of Yu Xinguo, who worked for a collectively-owned enterprise.

Under the pressure of debt, Zhang decided to restart her business to sell garment accessories in 1986. Within one year, the couple was able to pay off all the loans and became well-known in their communities with savings of more than 10,000 yuan, a huge sum in those days.

"At the dinner on the eve of the Spring Festival, we were extremely happy," the husband Yu said.

However, life always has complications. With ferocious competition in trading accessories, the couple decided to sell leather shoes.

But they paid dearly for their lack of experience in this field, and lost savings of more than 100,000 yuan in just one year and owed suppliers thousands of yuan.

In Zhang's dictionary, no word was more powerful than persistence.

The couple took a gamble and opened a shop in the China Qiaotou Button City in Wenzhou, which is a nationally-renowned trading center for small accessories. They rented a shop selling buttons in 1994.

In three years, Zhang and her husband repaid the loans and accumulated some new savings. In 1997, the couple shocked neighbors when they purchased a Volkswagen for 300,000 yuan, which was then considered a luxury item. From then on, her life was never again as hard as it used to be.