Flat tire due to the tire condition and had to pay $500

I felt real unreasonable that I had a flat tire absolutely for no reason, and they made me pay for the loss although I explained there were no sign of hitting anything, and that the road condition was absolutely clear. Despite of the insurance I choose to participate, I had to pay only $500, but without the insurance it would have been more. I understand I am responsible for the losses that I cause by my mistakes, but I was a bit surprised that I also have to be responsible for losses caused by the initial car condition, which should e taken care of by the rental car company. Although the company may offer a good deal for car rentals, I now understand that the price is only for the low quality of their car maintenance and hence the customers need to cover up for any losses including the company's faults. I highly recommend to opt in to the right car insurance program when you are renting from here.