In friendly matches, sometimes a team will not appear with their main players because the coaches of course give rest time to their main players to maintain the players' fitness and also avoid injuries during friendly matches. So it is not uncommon for coaches to play second tier players to give them playing minutes and also be able to monitor their improvement in quality. Yes, I agree with you that in friendly matches it is wiser not to place bets because the opposing team may perform better than them.
I think some people are sometimes able to read the conditions in terms of the game that will be arranged by the coach so that they will be ready to try their luck in the bets they place. Well, even though sometimes the odds are very attractive, I don't think that's a strong reference for betting on friendly matches if doubts surround our feelings.
That also depends on the level of gambling activity carried out by a person and most people prefer to place bets on official matches compared to friendly matches, but it is also not uncommon for people to use friendly matches to gamble. Rotation needs to be carried out in friendly matches so that young players have the opportunity to make their debut and coaches can also see the development of young players to be included in the first team in turn. That's why friendly matches are an opportunity for young players to show their abilities and perhaps it is appropriate for coaches to do that.
Gamblers have their own views when they place a bet, especially if the game is unbalanced, so after they analyze the match they decide to place a bet or not. Making predictions about an unbalanced match may be much easier because one knows who will win. Therefore, it is important to see who the opponent we are placing a bet on is because we will have an insight into the outcome of the match.