I have been added in a Telegram Signal Channel - Exchange's Arbitrage. [1]

Their aim seems very optimistic, since they want provide free information about arbitrage between crypto exchanges.
They provide very juicy opportunity (around 4-5% with only one trade in a matter of seconds!).

One of exchanges used for this arbitrage is called bitniex (I will not add a direct link) and it's a fake exchange with unrealistic price for all cryptocurrencies listed. Any pair suggested require always bitniex, and this is another bad hint.

There are several testimonial on the web of people that have already loss money. It seems that after the second withdrawal people are unable to take funds again. However it's a risk even deposit just one time since it could be possible in any time to get scammed.

Another scam that involves fake exchanges requires the offer of discounted crypto currencies. In that case people send regular deposit but they don't receive any crypto. 

When you see a buy or selling price too good to be true, please be aware most probably it's a scam.

Additional Notes:
[1] telegram channel "Announces Signal"
https://web.telegram.org/#/im?p=s1374615521_11159946188966393960

Binance ref code R145FEA used by admin in telegram

Medium Beginner’s Guide to Bitcoin Arbitrage:
https://medium.com/@arbitragesupport/the-beginners-guide-to-bitcoin-arbitrage-4475f4110822

This guide has been adapted from original post in bitcointalk here