Example 1:
Available credit...$34.00
Items purchased:
--$7.99 in new books (25% will be taken off - credit cannot be used with this purchase)
--$5.00 in bargain barn books (hole punched books - credit cannot be used with this purchase)
--$16.50 in used books
Amount of credit used...$11.50 (the first $5.00 is paid in cash, check, credit card)
Subtotal...$14.99 plus tax
Credit remaining...$22.50

The customer will be charged (the first) $5.00 with their credit being deducted thereafter. The customer, however, will be charged for the books (new and bargain), which cannot be applied to your credit.

Example 2:
Available credit...$34.00
Items purchased:
--$36.00 in used books
Amount of credit used...$31.00 (the first $5.00 is paid in cash, check, credit card)
Subtotal...$5.00 plus tax
Credit remaining...$3.00

The customer will be charged (the first) $5.00 with their credit being deducted thereafter.

Example 3:
Available credit...$17.50
Items purchased:
--$24.00 in used books
Amount of credit used...$17.50
Subtotal...$6.50 plus tax
Credit remaining...$0.00

The purchase exceeds the available credit, meaning the customer used all available credit leaving an excess balance to be paid in addition to the $5.00.

Example 4:
Available credit...$44.00
Items purchased:
--$7.99 in new books (25% will be taken off - credit cannot be used with this purchase)
--$3.50 in cash only books (handwritten price sticker - cannot can't be used with this purchase)
--$34.00 in used books
Amount of credit used...$29.00
Subtotal...$14.49 plus tax
Credit remaining...$15.00

The customer will be charged (the first) $5.00 with their credit being deducted thereafter. The customer, however, will be charged for the books (new and cash only), which cannot be applied to your credit.