Need Advice from Designers: Client Asked for Model File, Then Cancelled Project

Hello everyone,

I need some advice regarding a situation I recently faced.

A client posted a public project and I sent a proposal. I completed the requested 3D model, and then the client asked me to send the model file in chat so they could check it before accepting the project.

I delivered the model file, but after that the client stopped responding and later cancelled the project.

I have already reported the issue to support, but I wanted to ask experienced designers here:

1. Has anyone faced a similar situation before?
2. Is there anything else I should do now?
3. Is there any way to protect work after sending files?
4. What type of previews/files do you usually send before payment or project acceptance?

I am relatively new to project work, so I would really appreciate advice from experienced artists to avoid making the same mistake again.

Thank you.