Always remember that Mods and Admins do not PM first so if anyone PM's you claiming to be an admin or mod, you should at first check the group you share in common with them and get the tagged so take that other members would be aware of their acts then you can block them from your end so they do not contact you anymore.
That sucks in a telegram channel. And it seems every time I get into a channel with a lot of members, not gonna take a minute and some stranger will message me copying the admin/mod name.
That's just annoying. And it happens both ways (not just with newbies but also with group admins). I have been a mod in one or two channels in the past, and I'm talking from experience. You'll at least get one unsolicited PM daily if you are a admin or mod. You'll get tons of offers for promotional services. For example like, comments, ama sessions, social media marketing, shillings etc. There maybe some genuine offers but I consider most of them to be fake for which I know for sure, because you'll notice after a few days their account would just vanish. This is actually funny, there was this one time when a scammer pretending to be a game dev approached me and said, he wants me to test his new blockchain game (I don't remember exactly) and sent me the zip file. Nice try, lol..