What is the ruling on renting out a commercial register for a percentage of the value of contracts, with the lessor paying the resulting taxes and guarantees?

It is not permissible to rent out a commercial register, because it is akin to suretyship (guarantee), and the owner of the register is responsible for the actions of its renter before official authorities. The basic principle regarding suretyship is that it is a voluntary act for which no compensation may be taken, especially if the ruler prohibits it for a legitimate interest, due to the benefits it brings and the harms it averts. However, if the ruler permits it, and you undertake to pay taxes and the like, then you are allowed to take only an amount commensurate with your effort and expenses.