Here's what a "live one" looks like:
I called to make a solid date this evening. Around mid afternoon she sends me this text:~
"I can't meet you tonight, I'm so sorry. Can we do tomorrow? I'll make it up to you, promise."
Here's a dead one:
"I'm really sorry, honestly. I just found out that my boyfriend is cheating on me with another girl so I'm not just making up excuses. I need some time for me that's all. Would have been so nice to see you again, it's just not the right time for me."
She literally told you that this is not the right time for her, which for all intents and purposes translates to "I'm not interested".
You're right however, there is a skill to learn here. It's the skill of letting go of something you didn't have to begin with, and instead of wasting your time on obvious dead ends, invest it into someone who deserves it.
If you're confused about the call, people tend to comply when you put them on the spot. Ofcourse it's easier to say no over text than over the phone.
Some people will hold on to dying businesses and hemorrhage money because they simply can't cut their losses and move on. It doesn't always have to be a classical case of "madly in love" or any kind of emotional attachment even. Not having other options is sufficient enough reason.
Either way, learn to easily walk away and remove wishful thinking from your vocabulary. It'll take you a long way,