Then it's the same thing as just saying "no". Which isn't discrimination, but it's just logical. If the market price for renting is 1000, and I ask you for 1000

Then it's the same thing as just saying "no". Which isn't discrimination, but it's just logical. If the market price for renting is 1000, and I ask you for 10000, that's basically a "no". And to give some glimpses towards answering your question, the basic answer is the laws, and information asymmetry. I am only aware of the local situation, but the law is strongly, to the point of unfairness, in the side of the tenant. And in sum, the owner has less than 1 hour to judge psychologically if the person in front of him is trustworthy. Something that is easily faked.