Probation period is a period in which employers can discreetly evaluate candidates' achievements and candidates also can assess employers and the company as well. Probation period is a common practice in the working industry. We need to completely understand that it doesn't mean even after probation period ends, there will be increase in salary. Everything depends entirely on the early discussion between the employers and the employees. 

Usually, there will be increase in allowance, commission, workers benefits or perhaps merely 10% increase in basic salary for entry level position. Thus, employers need to provide new offer letters or working contracts in order to validate the working statuses of the workers.