The number to watch
Warranty claims traced to invoices. Tank warranties run for years and the claims arrive without paperwork. The useful figure is how many you could actually match to a bill — because every one you cannot is a replacement you absorb rather than pass to the manufacturer. Once the brand, capacity and layer type are recorded on the invoice and searchable by party, that number goes to nearly all of them, which for a dealer selling volume is a serious saving.
Capacity, layers and brand on the item
A 1000-litre triple-layer tank and a 1000-litre double-layer tank from the same brand are different products at different rates, and the customer chose between them for a reason. Keeping capacity, layer count and brand as part of the item means the invoice records exactly what was supplied — which is what the manufacturer will ask for when a warranty claim comes in years later.
Delivery and installation are chargeable
A tank goes on a vehicle and often onto a roof, and both cost you something. Charging a single delivered-and-fitted price hides that and makes your tank look expensive next to a shop quoting ex-shop. Separate lines for the tank, the delivery and any fitting or stand keep your material price comparable and your service visible, and let you see whether the fitting work is actually paying.
Warranty and the return three years later
Tank warranties run for years and the customer will arrive with a leak and no paperwork. If the invoice recorded the brand, capacity, layer type and date, you can find it by party or by item in seconds and deal with the manufacturer properly. Shops that cannot find the bill end up absorbing the replacement, which is a large cost for something a search would have answered.