Karcher S4 Sweeper

We bought a manual sweeper from one of Karchers suppliers, only to have it broken within less than 3 months after purchase. The machine has technical specifications indicating a max area performance of 2400m2, and with this in mind I purchased the machine to cover an area of 1000m2 on a daily basis. When returning the machine for repairs, I received an invoice for more than I actually paid for the machine a few months ago, reason being normal wear and tear. when I raised my concerns around this, the reply I got was that this specifications does not indicate the durability of the machine and that it is only supposed to be "used for an hour or so over weekends" No where was this explained by the sales staff when purchasing the item or there any indication on the item that it is not suitable for daily use.