“Fair tax” is a species of consumption, (sales) tax. I’m aware of no simpler administration and enforcement of a general sales tax than the “value added tax”, (VAT).
The United Kingdom’s collectors of VAT are the “HM Revenue and Customs”. They are comparable to USA’s IRS. The experience of the UK and all nations employing consumption taxes indicate government’s sales tax collection expenses will be less (than for income taxes), but still of significance. Fair taxer’s hopes of severely downsizing or eliminating IRS’s functions are unrealistic.