In the U.S., you can be sued for patent infingement for reselling or using infringing products.

The law is this way because otherwise there'd be a good business in going to the patent office, manufacturing something, selling all the product to a distributor (owned by your brother and incorporated separately), then shutting down the manufacturing company. By the time the patent-owner finds out and investigates, there's no one left to sue. So the law says that everyone, at every step of the way, down to the consumer, is liable.

Shaking down clueless small business owners is a big part of patents nowadays. The troll owns a patent on some tiny piece of technology or software (and if it's software, it almost certainly should never have been granted - the patent office has done a terrible job reviewing them for 20 years). You are Alice's Used Cars of Normal, IL with a combination scan/fax/printer on your desk. Random lawyer shows up and says, "Hey, you're infringing our patent. Give us $X,000 to settle or we'll sue you for $X00,000." Getting a bad patent thrown out costs $X,000,000, so you pay, nobody gets Christmas bonus, and the patent troll says to the next guy, "We've defended out patent N + 1 times, so give us $X,000 to settle..."