How does someone get away with writing false paychecks to someone just so that person can file a tax return to get money back at the end of the year?

People get away with all sorts of things all the time, because there is only so much money that can be spent on hiring investigators to look into everything that everyone is doing, to make sure that they are not getting away with anything. In the case of income tax fraud, most income tax returns are not audited, because there are not enough auditors, or enough money to hire enough auditors, to audit everybody. Most of the time, society operates on the presumption that people are honest. Many people are not honest, but so far it is just not practical to watch everybody all the time. Perhaps in the future there will be better surveillance technology which will make it practical to do that, and people will no longer get away with things. I can certainly imagine sophisticated accounting programs that would allow computers to automatically audit all income tax returns and to detect the kind of deception which you mention. So far we don't have that.