OP is like, "Hey, we need this flash btc and contact us to telegram so that I will disclose the details there but not here".

Also, "I've got a brand new account and whoever goes first is the one whom I will trust but that's already the pay".

We're not born yesterday and whoever goes into this likely scam will regret his actions. Understanding the term flash btc is likely you'll give him your btc in a flashily way and its gone.

Once is enough for scammers to do their scheme. Do it with middleman/escrow to have safe and secured way of transaction. Else you won't get anything from here and no one will be get fooled, especially for a someone try to lure in telegram way of scamming.

So what legal work does flash BTC do?

Seems like you are trying to look for someone to scam but fortunately for us here members are woke. If manage to scam even a Satoshi out of someone here, I will be damned.