Instead of just having invoices and tickets, also have a "Order" option that allows you to place an order, take a deposit, link to a PO, then when a product arrives, convert the Order to an Invoice, which satisfies the General Ledger account. Basically the "Parts" option, but with inventory tracking. This way orders for computers, accessories, etc, aren't blended in with your Tickets, and aren't "Invoiced" before the product arrives or leaves your store (which thus removes out of your GL acct)