The car rental company was good, they didn't try to upsell me. Since I was going to stay in Bangkok for a day and then drive nearly 2000 kilometers, I proactively inquired about and purchased their full insurance for 60 yuan per day, which is not expensive. I recommend getting this if you plan to drive in Bangkok. Many roads there are narrow two-way streets with lots of motorcycles, and since the road conditions are unfamiliar, it's easy to get into minor accidents.