Is it common for a client to send a freelancer a resoundingly positive response to a proposal, but then vanish? I've had a couple of people send me "yes, we want you! Do you still want to work for us? We hope so!" kind of messages. I've replied "Yes, ready to start when you are", but am still waiting. It's odd: I'd love the work, but the people are not responding.
I've had a few of those, but most of them turned out to be caused by delays on the client's side. I waited a week or so and then contacted the client to ask whether they filled the position and if I should withdraw my proposal. The ones who answered mostly still wanted the work done but were waiting for documents, specifications, budget approval or other things like that.
It has not been my personal experience that potential clients send a "we'll hire you" and then disappear.
My responses come in two flavors:
A. They interview then hire me.
B. They are spamming scamming and interviewing a plethora of applicants (personally, I avoid those jobs for several reasons). But, I'm a data/research nerd and I always go back to see how many invites they've sent/how many freelancers they're interviewing.
However, there's always the possibility it is different for others depending on many factors including the industry in which they're freelancing.