Please read Roman Tax Farming. The best strategy for the governor is to appoint the wealthy landlord as the tax farmer, and authorize the tax farmer to take whatever actions are necessary to collect the required tax.
aside: I haven't actually double checked this against the reign of Hadrian; someone more skilled in Roman history could potentially serve me up....
The governor set a tax level for the province - I want a million sesterces this year. You go get it. The publicani could write a check for a million sesterces, or he could go out and shake down all left handed red haired me, or whatever he wanted. Note that the Publicani was expected to make a profit - if the Publicani needed to collect a million sesterces, then it was legitimate to collect a million and ten thousand and call that a profit. Under this system embezzlement was fundamentally impossible. Aside: there was a limit - publicani competed for the privilege, and the candidate with the slimmest margin was theoretically selected.
The actions of the publican were prima facia legal because they were authorized by the governor. Anyone who complained about the procedure of tax collection was referred to the governor. I don't recall off the top of my head, but I believe that there was no right of appeal (there were informal channels to Senatorial patrons, but no formal right of appeal)
Remember that by law the governor was immune to prosecution during his term of office. The one time that a governor was prosecuted after his term of office,
his defense lawyer had him acquitted on the basis (rough summary)"Each of you would have done the same; it cannot be corruption if it is common practice"
Why keep receipts and records at all? Competition between publicani was fierce, and those who kept records tended to be more efficient. They didn't fear audits or embezzlement - those concepts were meaningless.
Please also consult - for a fairer, more complete, less cynical treatment: