I buy mostly from liquidators, where everything is sold as-is, but that doesn't stop end users from trying to make a claim, so many manufacturers often have methods for marking items that are not covered by the warranty. For example, Ryobi brands the items with a plastic welder, leaving a tell-tale wavy mark.
A robust liquidation market does a lot to prevent waste, and it reduces the cost of living for those who participate, so finding ways to allow products to be truly sold as-is is vital, otherwise the next most logical option is to put those items in a landfill.
It's also important that there's no legislative hurdles to seelling items as-is, or there may be no legal way to sell a salvage products without completely overhauling them, which is usually not cost effective.
> so many manufacturers often have methods for marking items that are not covered by the warranty
With textiles this is usually a hole punch or something with the tag. With hardware we had the serial number recorded.
But consumers don’t care. If they buy something from a vendor they think is selling them something as new and the vendor tells them to go the manufacturer, the customer doesn’t care that you marked it as not eligible for warranty. They just want that coverage
We even had customers write ragebait Reddit posts claiming we were unfairly denying warranties, people sending stories to popular newsletters and journalists, and other attempts to make us look bad for not honoring warranties on products they bought through gray market channels.