Often times the only thing you can do is walk away. When individuals have no understanding / concept of time or they simply don’t care a choice has to be made.
I think about it as business to consumer versus business to business. B2C is about status. B2B is about lasting relationships. By default, anyone searching for services on freelance aggregators is using a B2C model. Status can be about spending lots of money, but it defaults to being a saavy shopper or hard negotiator and such. Basically people with a B2B view of web design and lots of projects already have a relationship with a design provider.
People on the freelancing aggregators are businesses. It really often comes down to being able to do what you can afford to do. When a client doesn’t understand the time it takes to put together what looks good, often there can be an ultimatum. It’s extremely hard when the individual doesn’t have concept of time or design.