Classic. Telegram is full of scamers. the best way is ignore them cause they have million of fake accounts. the most popular way - pretending to be an exchange admin. after joining Telegram group they will text you private with questions - how can i help you etc.. even if u dont have any issues.
Thats really annoying.
Although telegram is one of the best app to get updated information about crypto currencies projects but many people misuse this and pretend to be the owners of certain ico or other famous persons and demand money from them in return of some investment or schemes. Newbie traders or those who are recently involved in bitcoin easily get trapped by them and they scam money from people.