Some personal auto insurance policies do not cover rental cars that are being used for a work / business purposes instead of for personal use such as a vacation or as a replacement vehicle while your car is in the shop.
When you rent a car, most personal auto insurance policies coverage transfers over to the rental vehicle during the time the rental is used by you. However many insurance companies have restrictions on what is covered on a rental car with your coverage and may possibly have conditions on the reason you are using your rental car, such as if you are using the rental for business instead of personal use.
Since personal auto policies that provide coverage for rental cars often include conditions read through your policy and then speak to your insurance agent for clarification of your coverage on rental cars. For example, your car insurance may cover a rental vehicle for vacation purposes but not cover rentals used on business trips and may limit coverage for long-term rentals. Personal policies also may not cover rentals in foreign countries.
If you find that your current car insurance policy does not cover a rental car for your needs then you can shop around for low cost auto insurance here that does.