It's very easy to impersonate on telegram, In fact that's where most of the scammers lies. I've been approached more than once but I find it easy in recognizing them.

A username can also be changed on telegram. A scammer can decide to use your username and DP just to scam another fellow.

But, what people don't know is Telegram has a code for each user. This can't be changed, if you check the user profile, you will notice a code beneath the username. What I do is compare these codes with the real owner (that's if I have his/her telegram username) before proceeding to chat.