Can someone buy something as worthless as $0 just like your Telegram account?
There's a market for this, usernames like this are sold
Some names are sold for 100k dollars
https://fragment.com/
Telegram allows people to buy username but it can only be done through their marketplace called fragment. I mean it can be bought only on Telegram marketplace called fragment.
Your scam is not new at all.
Calling someone a “scammer” outright is premature.

Using non-official deal like direct may chance to risky, but it only becomes a scam when there’s clear theft or proven loss.
For deal safely OP and buyer, you can simply share your direct Fragment link, for example: fragment.com/"yourusername", and promote it here.