There is no bet in gambling that is 100% guaranteed to win, even if I saw a match like in your example, when Real will play against a weak team from the fourth division, I would think that there could be some kind of catch, and if I made a bet, then as small as always, I would definitely not increase the bet even if I thought that Real's victory in this match was almost guaranteed. When a player is more confident in some bets compared to others, this can play a cruel joke on him.
With any form of gambling, the risk of losing is always greater than the chance of winning. For example, in sports betting, where a strong team plays a weak team, many people may be confident in betting on the stronger team, but that doesn't mean they can't lose.
Regardless, when gambling, it's best to consider your betting capabilities, such as betting within your means, and not wagering beyond your means, which could significantly impact your finances.