I think the other way to know the real "TELEGRAM" account for every trusted member who also using TELEGRAM better to give their ID Telegram Account and not only the username. This could be a good way for every trusted member who gives an option communication outside bitcointalk one of them is Telegram.
Here a few steps to know and checked ID Telegram Account
1. Trusted member need to know his ID Telegram Account.
2. To know your ID just us a bot who provide to reveal information of ID Telegram Account, I recommended everyone can use @userinfobot
3. Just type /start then your account information will be revealed.
4. Trusted member, give his ID Telegram Account on their thread service or other things.
5. The client or other people verified the ID Telegram Account by using @username_to_id_bot just send to the bot a username telegram, so he can make sure communicate with the real person.
6. Then the bot will reveal information other people ID Telegram Account.
Just match it with the ID Telegram Account from the trusted member, every account telegram has their own unique ID Telegram Account.