What this market does is that it adds or subtracts some goals from a certain match and such that it appears as if one of the teams is either trailing or leading by some goals. Most of the time, the weaker team is the one awarded the goals so that it can start the game with some few goals.
The punter who places a bet on this wager has to be careful since the goals margin should not be the same as the number of goals that the weaker team was awarded. The favourite team needs to win otherwise the bet will just go like that and the punter loses it. For example, if a team was given something like 2 goals at the start of the game, and the punter chooses to bet on the big favourite to win the match, then that team needs to score more than 2 goals in order to win the punter the bet. If the team only wins the match having a winning margin of only 2, then that will not be very helpful to the punter as the punter will have lost that bet by default.
So, punters have to be very careful by the number of goals that they are going to award the weak team. If they award then too many goals, then they risk losing their bets. A safer handicap way is by awarding the weak team not more than 2 goals. In fact, only one goal is enough.
Taking a case in which Team A is stronger and Team B being weaker, if the punter has to go the handicap way, then he/she should award Team B only 1 goal and hope against hope that the other team (Team A) score very many goals against Team B. if that is not the case, then the punter will lose that bet no matter the outcome of the games.