What is/are the method(s) applied in determining the receivables? And if any which of method is more efficient?

QUESTION NOT CLEAR  BUT THERE IS NO METHOD TO DETERMINE THE RECEIVABLES GENERALLY SELLING GOODS TO CUSTOMER OR SALE ANY OTHER SERVICES OR RENT RECEIVALBES ETC HAPPENING WE ARE DEBIT THE CONCERN PERSON WITH THE FIXED AMOUNT THIS AMOUNT CALCULATED BASED ON THE SALES VALUE OR SERVICE VALUE