I am looking at a 2018 sedan that is priced well below market value. The seller admits it was in an accident but claims it wasn't serious enough to total the car. However, I have heard that insurance companies sometimes declare a total loss even if the car looks fixable. How can I verify if this car was actually written off financially before I buy it?

You are right to be skeptical, as the definition of total loss varies by state and insurance policy. A car can be declared a total loss if the repair costs exceed a certain percentage of its value, even if it looks drivable. You should verify the specific loss history to see if it hit that threshold. You can read here about how total loss is determined and get a report to check if this specific VIN was ever marked as a financial write-off.

Insurance companies really can declare a car a total loss even if it looks totally alive and drivable on the outside. I’ve heard about cases like that, and it’s probably very individual.

I’d advise first of all not to panic and just check everything carefully. In general, things like this can be clarified pretty quickly with VIN reports. I personally recommend FAXVIN, everything is done fast there, and the info comes from official sources, government registries, and insurance companies. The report will clearly state whether there was a salvage title, total loss, insurance write off, which insurance company was involved, and the date and reason for the write off. If the car was written off financially, it almost always shows up in a VIN report, even if it was restored later. So yeah, a VIN report plus title status plus an independent inspection is the minimum set when buying a used car.