Where do I indicate write offs and adjustments for client non-payments?

[tracybryan]

Also, where do I indicate refunds made to clients?

[DDollar]

Unless your business is on an accrual base and you recognize income when you invoice a client or make a sale (instead of when you are paid) you don't make an adjustment for client non-payments.  Most taxpayers use a cash basis.  If you are using the accrual method, you create an expense for "Bad Debts".    As for refunds made to clients, you reduce the amount you are reporting as income, or you enter as "Returns and Allowances".