I am using this bot to get id by username: @get_any_telegram_id_bot
And for many accounts it returns same id. Is it by mistake? It returns this id only for account which I would call "suspicious" - like black market and so on.
How can this be explained? Bot bug? Or it returns this id for accounts marked in some way?
user_id is supposed to be unique, and it's most likely the bot implementation cause.
How they even receive user ids is a big question; methods for that are a bit hacky. It could happen for instance, that the bot keeps a database of user ids fetched in some hacky way (ways), and returns some id because of some data corruption issue.
Of course, that all would be a guessing game until we see the bot's source code, which seems to be unavailable.