Refusing service after being called up means no leaving the country or going back to school for two years, and no civil service or state-owned company jobs

In plain words

If you sign up and then refuse to go, the consequences come in a string. You can't be hired as a civil servant, and state-owned enterprises and public institutions (事业单位) can't hire you. For two years you may not leave the country, enroll in further study, or return to school. You are also put on a list of people seriously untrustworthy in meeting their national defense duty. So “sign up first and back out if it doesn't work” is a very expensive idea.