that's crazy. Also so many people trying to apply fraudulently... I was also told by a friend who is a visa agent that they will soon tighten the checks when re-entering the country with DTV. Like checking your account balance for example...
I also work only with Upwork. I added a letter explaining what is my activity, that I work on Upwork, where my clients from etc. plus added screenshots of my Upwork public profile with earnings and reviews. Plus screenshots of my own website showing the services.
if the embassy knows your flight date they will ask you to show them a ticket to Thailand at a later date. If you can't provide that your application will be refused
If you put a travel date to Thailand in your application that is already passed they will ask you to show a plane ticket to Thailand at a later date or refuse your application