“And when he had agreed with the labourers for a denarius a day, he sent them into his vineyard.”
In this case the estate owner agreed with the workers whom He hired from those who were standing there, a fair wage for a day's work, one denarius. Then He sent them to work in His vineyard, no doubt under His manager (Matthew 20:8). The labourers were quite satisfied. He had offered them the usual rate for the job. That was important. God cheats or underrates no man.