What isn't covered?
The plastic caster wheels as you can see a set of four is worth $9 dollars. This wheels are cheap low quality wheels made of material using cheapest plastic called Polyethylene. Polyethylene comes in fours densities; low (LDPE), medium (MDPE), High (HDPE) and Ultra High Molecular Weight Polyethylene (UHMWPE). Then hardening it with polyamide. Even Polyamide plastic is not strong.
What is covered?
Instead you want to purchase rollers like the example in the last image "Heavy duty Rollerblade style caster wheels."
Western Express Moving Ltd moves cheap material all the time with zero problems. However, when it comes to liability, as a quality company we prefer moving quality material. We will not risk our reputation over cheap items, we would be wrong company to go with! Here are examples of carts that usually come with low quality cheap caster wheels. We've moved high quality gamer computer chairs with each wheel costing $50, compared to the set of four caster wheel for $9 from ULINE CANADA.