We are using thousands Telegram account which registered with thousands virtual numbers, so the chance of block/ban/delete or flagged by scam is not our problem. It never been happened but In the worst case if this happens, our customers' business will not be affected and we will most likely lose only a few Telegram account which is related to us.
So how's the conversion, the community is advising against unsolicited messages and there are account settings that will not allow receiving of messages, I'm one of those who do not accept unsolicited emails, if not part of my contact.
I just hit block and delete for any incoming messages so that would be wasting a lot of 20 cents for every block message and there's no guarantee of conversion either.
Part of ethical business is avoiding spamming because it will harm the reputation of the projects, literally, you are promoting projects through spam which is not good.