Yes, Telegram is known as the empire of online scammers, and if we still have someone who trusts a stranger's claim on this forum, then the person is not worth being in the online space.
Scamming activities like this don't happen only on Telegram, so people need to be more careful on every social media platform, not just Telegram, because online thieves use different strategies on different social media platforms.
Assume we consider buying/selling Telegram usernames, there's an official website where this can be done, so it should be understandable that any individual trying to offer a service outside of the official marketplace created by the Telegram team is up to no good.
Exactly Telegram is place where many online scams happen. We should definitely be careful if someone on there tells something that sounds too good. It is almost shocking that people still get tricked by those obvious scams.
But it is important to remember that scams are not just on Telegram. Bad people try to trick on all sorts of websites and apps.
Telegram has official place to buy and sell usernames so if anyone tries to sell you username in different way outside of that official place we should know they are probably trying to scam. It is big warning sign.