In most workshops the customer account is kept in a separate book or a separate spreadsheet. The order is in one place, the payment in another, the balance computed in a third. The arrangement holds for a while; then one day the customer says they already paid and the two records have to be compared.
The job of a glass customer account system is to prevent that drift from the start. The balance is not a number kept on its own but a result derived from orders and payments. When the order amount changes the balance changes with it; when a payment is entered it is visible which job it answers. There is no figure left that someone updates by hand.
In daily terms this means the question of how much a customer owes is a reading rather than a calculation. Months later, when someone asks about an account, the answer is read from a single place and nobody has to lay two lists side by side.
Overdue balances becoming visible comes out of the same structure. Because the dates are in the record, late balances surface by themselves. In a book kept by hand this is only noticed when somebody sits down to look, and it is usually noticed late.
The head of the chain is still the quotation. If a glass quotation system turns an approved quotation into an order without creating a new record, then the customer account feeds from that same record. Where the amount came from is written in the list a glass pricing system holds; what sits underneath it is the work of a glass costing system. The three are not separate programs but different views of the same record.
It matters that the payment shows which job it answers. With a customer who pays in lump sums, if it is not clear which order closed, the balance is right but the picture stays blurred. Writing the payment onto the record removes that blur, and a question asked six months later is answered from a single screen.
That wholeness is what to look for when searching for a quotation system for glass workshops. Individual screens are easy to write; the hard part is the same number staying the same across four screens. Once that holds, inconsistency disappears, because inconsistency usually comes from typing something a second time rather than from bad intent.