Credit
Okay for example a buyer buys the product of Rs.3600 on may 1 and he pays only Rs.3000 so the credit in the particular transaction remains Rs.600 but the vat and billing will only be done for the amount paid i.e. Rs.3000 and on today's earning and transaction only Rs.3000 Will be seen.
Now if the buyer pays the amount of Rs.600 in may 5 , the billing of Rs.600 will be done on may 5 and the Rs.600 will be shown on transaction of may 5.
Bad Debts
If the credits are not paid with in 2 months or for the certain amount of time the credit will move towards bad debts.
But also remember the bad debts can also be paid same as credits.
Partners
A sellers can also add the information of the importers he imports from while adding the items the seller can select the importers he added the product from.
You can also add the total cost price while adding the item so the profit could be calculated and also you can separately calculate the VAT to be paid to government.