Best way to know if the text is a scam or not is when you received that you've won something or have been picked for a promo when you didn't join/participate in any kind of contest at all. This only means that someone just sent you a random text from their spam directory. Best thing to do is to block their numbers and delete their messages for you to avoid on accidentally viewing them. Just remembered that if you haven't participated on something and you receive these kinds of messages best is to avoid it.
But imagine if the SMS comes from someone pretending to be a representative of a brand you often buy. Imagine you just bought yourself a new pair of sneakers and you are getting a 50% discount as a promotion for your loyalty. People could easily fall for that.