Upwork is a weird place. In my downtime due to this whole Covid thing, I’ve been experimenting with it. It’s definitely a step up from most crowdsourcing sites in that nobody is supposed to give clients ideas prior to a contract based on the designer’s proposal and portfolio.
Even so, most of the jobs posted there are really iffy, oddball projects. Most potential clients are tire kickers who are just testing the waters and never end up hiring anybody. Most have little to no experience working with designers (or any creative), and have no idea how things normally work and that designers actually need to earn a living and don’t just work for fun.
So in the situation you spelled out, this person is making a habit out of soliciting free ideas from people, then choosing which, if any, he/she will pay for. This kind of potential client is best abandoned.
Over the years, when I’ve had people approach me asking for spec work before proceeding, I’ve usually told them that we can sign a separate contract obligating them to pay me a fee for the ideas with the option of them cancelling any further work if they don’t like the ideas. Most (not all) won’t even agree to that. They’ll think little of dropping off their Porsches for a $2,000 afternoon service, but act shocked when a designer expects to be paid for every hour worked. I don’t quite get their thought processes, but it’s best not to work with them.