Is it permissible to increase the agreed-upon percentage with the office owner in exchange for his guarantee to pay the amount to the factory owner?

It is not permissible to take a fee for suretyship or guarantee, as this may lead to falling into usury (riba). The guarantor is obligated to pay the debt on behalf of the guaranteed party, and if he pays it on their behalf, that is a loan. The fee for the guarantee would then be an interest on the loan, which is usury. Jurists have stipulated the invalidity of suretyship if a payment or compensation is stipulated therein, because it resembles a loan that draws a benefit, which is forbidden by Islamic law.