We have a vehicle repair business.

Question

We have a vehicle repair business. Often we use customers' cars to drive home as this allows us to test-drive the car as well as go home and to the masjid for salaahs. Sometimes with the same customer's car, we take tools home when needed. Sometimes if the customer's vehicle is a bakkie, we use that bakkie to pick up building supplies etc. We subtract some amount from their invoices but do not inform them. Are any of these actions jaaiz? Sometimes inevitably, some minor damage is caused to the customer's car. (like denting and scratches). We subtract from the customer's invoice proportionately without informing the customer. Is this jaaiz? Is there any other way to avoid confrontation? Customers are sometimes unable to pay for the repairs done to their cars. In most cases, they end up selling their car to us or we take possession of the vehicle during which time a storage fee is levied (we have sign boards stating this). In this case, is it permissible to sell/ scrap the car to defray expenses? These vehicles are often kept for years without contact from the owner.