One thing to note is that governments themselves are, by definition, rent-seekers. This is inherent to how a government - a monopoly on the legitimate use of violence within an area - works. Once you are sovereign within a territory you can extract rents in the form of taxes, and if you don't extract enough you will be deposed by someone who does.
Most governments also tend to encourage their own industries to rent-seek as well. If your country needs heavy industry or scientific research or cultural behemoths, it's far easier and politically defensible to construct new narrow property regimes (e.g. copyright, patents, PDOs, etc) for those companies to exploit rather than just paying them subsidies. These regimes can be selectively weakened when you need to build your industry domestically (what the US did to the UK, or what China did to the US) and then strengthened later when you need to protect it internationally (what the US forced into WIPO).
Very little of capitalism is actually adding value, in the sense that you have a business that hires people, buys materials, and turns them into goods and services at a prevailing market rate. At the lowest rungs of the chain, sure - you might have, say, petite-borgeouis crustaceans hiring workers to cook food and sell it to people who need it. But that's not where most of the actual profit is. Compare that to, say, a fast-food franchise; which doesn't usually run any restaurants or sell any food. They instead sell trademark rights and supplier relationships. In particularly egregious systems like McDonalds, they even rent their franchisees the land that the restaurant must be housed in.
Left-wing critiques of capitalism are typically extra-cynical about this, and would consider even the small profit Mr. Krabs makes on burgers to be rent, not value. This is usually in the context of the employee-business relationship, however; not the business-customer one. Small businesses generally don't extract a premium on the goods or services they sell just because they're the only company that happens to own a stove or know some secret recipe. But in the context of employees, they are getting paid less for their labor, albeit in exchange for not having to bear up-front capital costs or deal with inconsistent revenue. Whether or not this constitutes rent or value is most likely a political opinion, not something that you could actually devise some economic criteria for.