Quoted from sunnRAT:they just go absolutely mute. So I end up waiting for a response that never comes.
Stop waiting for a response. I've found something like, "Let me know before Tuesday if you want to make a deal. Talk to you soon," works well.
People change their mind and have different priorities all the time. This should not be a surprise. If you give the other party in any transaction the power to stop and hold indefinitely some will inevitably do that.