need to consider your overhead costs, employee salaries, utilities, taxes etc...etc !!!
If you only have one borrower in a day ... then your business is losing...
I tried that one time... borrowed 500 bucks , you issue check for 551 foe two weeks maximum. either you redeem it on the specified date or it will be encashed by them in the bank ! u need 24 hours after paying to be able to borrow again!