Many times I have seen a job offer saying they're looking for a long-term freelancer for an on-going project but they posted it as a fixed price job with a complete-by date.
So technically you'd doing this long term job, and in total be paid $20 for it, or it says a budget and then asks you for an estimated duration, and for the amount of money offered, you write fitting duration. But what if that duration is a week? And then client dismisses you as a long-term potential?
Of course, there is a way to change the type of the job myself or suggest it to the client.
But is there a way to prevent it in the first place? It's hard for freelancers to submit a proposal.
Clients who say things like that in their posts are usually just on a fishing exposition to see who they can snag to do their work cheap. When they find their cheap contractor, they will string them along with vague promises of long-term work and higher pay to get more work done than the original description implies. More often than not, they have no intention of hiring the contractor for "long-term" work.
Once they have the work that was done for the original job - and done cheap - they will post the next task they need in a rinse and repeat process hoping to snag another contractor who is willing to work cheap based on the same vague promises. In a word, they are "users" gaming the freelance system to save a few bucks on their shoestring budget. In my experience on Upwork, as well as with my private contracts, it's usually best just to pass by any client who implies anything about long-term work.
This may not always be the case, but it's safe to say it is the majority of the time.